United States: ‘Keep Out’ Signs Can Override Open Internet Culture

The Internet gives every appearance of being wide-open, public, available to all. You can email anyone in the world who is connected to the Internet. You can visit any public website. This amazing network — a "universal space" in the words of Tim Berners-Lee — seems as accessible as a public park.

But can you put legal locks on Internet doors? Can public sites (not just password-protected sites) create legally enforceable selective admissions policies? Can email systems and websites use law to exclude unwanted messages and unwanted visitors?

Yes, such locks are possible, and a recent decision from the U.S. District Court for the Northern District of California has even recognized a potential new locking mechanism: the Computer Fraud and Abuse Act. Still, the decision faces strong objections from those who believe these legal locks "implode the basic functioning of the Internet itself."

Several twists of Internet law allow legal locks on otherwise public Internet places. The cases are developing, and the decisions haven't yet settled on any all-embracing principle for the circumstances in which a public place on the Internet can or cannot exclude particular unwelcome visitors, or particular kinds of unwelcome visitors.

Blocking online 'scrapers'

The concept was first tested when automated computer programs began scraping public Internet sites for data, which would then be reposted or otherwise used by the party that conducted the scraping. In one case, Bidder's Edge, a website operator, sought to create a portal that would compile offerings on multiple auction sites, including eBay. eBay sued, claiming that the compiler's automated program (its "robot," "scraper" or "spider") overused eBay's resources and slowed down its operation. The court sided with eBay in 2000, ruling that by continuing to scrape eBay's site after it had been warned not to, the compiler had committed the tort of "cyber-trespass," an electronic version of the centuries-old tort of physical trespass. Several other decisions around this time period took similar approaches.

The cyber-trespass tort has practical and free-speech limits. When a dissident former Intel employee directed thousands of emails to Intel employees, Intel sued, characterizing his conduct as cyber-trespass. But the California Supreme Court disagreed, finding an insufficient physical effect on Intel's computer system from the emails, and holding that disruption attributable to the content of the emails could not support a cyber-trespass claim.

Robots keep out

One of the key lessons from the initial round of cybersquatting cases is that the party that wishes to shield its otherwise public Internet facilities from certain parties, communications, or uses, must give clear notice. Just as visitors are usually presumed to have the right to approach your front door and ring your doorbell unless you have posted "no trespassing" or "keep out" signs, public Internet sites are presumed open to all, until that electronic "keep out" sign is posted.

But what is an adequate "keep out" sign? There are a variety of ways to post "keep out" notices, both general and selective, on the Internet. One of the simplest and most basic is a robots exclusion file, which appears in source code (and is often informally referred to) as "robots.txt." Automated scraping programs (robots) are supposed to look for each website's robots.txt files, which give instructions as to whether all or certain robots are excluded.

In an unusual case in 2006, Field v. Google, a website operator sued Google, claiming that Google, in regularly surveying the Internet to update its search database, made unauthorized copies of the operator's site. The court, however, noted that Google honored robots.txt files and found that robots exclusion files were well-known and well-accepted techniques. The court ruled  that the operator had no claim because he could have so simply signaled to Google that his site was off limits. At least from this court's view, robots exclusion headers work as "keep out" signs, and if you wish to keep robots off your site, you may even have an obligation to use them.

Cyber-trespass claims are viable, and robots.txt files serve as effective "keep out" signs. One might, therefore, expect many cyber-trespass cases. But there's a catch. Cyber-trespass claims generally require a significant physical effect on a computer system. With the enormous improvements in the speed and capacity of computer systems, the likelihood of such physical effects have diminished. The faster and more robust your computer system, the less likely it is that you will suffer the physical effects from a robot that are essential to a cyber-trespass claim.

Craigslist v. 3Taps

That may explain why, in a recent case reminiscent of the eBay situation of a decade ago, the federal computer anti-hacking law, the Computer Fraud and Abuse Act, was asserted against a scraper. In this case, Craigslist objected to a scraping service, 3Taps, which scraped, aggregated, and republished its ads. Craigslist notified 3Taps that it had no permission to scrape the site. And when 3Taps continued to scrape, Craigslist sued under various theories, including the CFAA, which prohibits "unauthorized access" to covered computer systems. (The act's coverage of computer systems is quite broad, and included Craigslist's servers.)

The court found that Craigslist had clearly barred 3Taps from its website, no differently than a store owner who decides to prohibit a bothersome guest from entering his store. "The law of trespass on private property provides a useful, if imperfect, analogy," U.S. District Court Judge Charles Breyer wrote. "Store owners open their doors to the public, but occasionally find it necessary to ban disruptive individuals from the premises." Craigslist's unambiguous "keep out" notice, therefore, perfectly set up the case against 3Taps. Defiance of the notice by 3Taps clearly implicated the CFAA's prohibition of unauthorized access to computer systems, the court held.

Finding the CFAA's application clear, the court gave short shrift to 3Taps' plea that its ruling went against Internet culture and that a "permission-based" regime "could implode the basic functioning of the Internet itself." Faced with "unambiguous statutory language," the court found that Craigslist had full rights to selectively revoke authorization to access its website.

The decision was issued in the context of a motion to dismiss, so it holds only that a CFAA claim is plausible in these circumstances; whether 3Taps is actually liable will be determined at trial, based on all the facts and circumstances. And, of course, it may take an appeal in this and other cases to fully resolve this new CFAA theory for "keep out" signs on the Internet.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

To print this article, all you need is to be registered on Mondaq.com.

Click to Login as an existing user or Register so you can print this article.

In association with
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Register for Access and our Free Biweekly Alert for
This service is completely free. Access 250,000 archived articles from 100+ countries and get a personalised email twice a week covering developments (and yes, our lawyers like to think you’ve read our Disclaimer).
Email Address
Company Name
Confirm Password
Mondaq Topics -- Select your Interests
 Law Performance
 Law Practice
 Media & IT
 Real Estate
 Wealth Mgt
Asia Pacific
European Union
Latin America
Middle East
United States
Worldwide Updates
Check to state you have read and
agree to our Terms and Conditions

Terms & Conditions and Privacy Statement

Mondaq.com (the Website) is owned and managed by Mondaq Ltd and as a user you are granted a non-exclusive, revocable license to access the Website under its terms and conditions of use. Your use of the Website constitutes your agreement to the following terms and conditions of use. Mondaq Ltd may terminate your use of the Website if you are in breach of these terms and conditions or if Mondaq Ltd decides to terminate your license of use for whatever reason.

Use of www.mondaq.com

You may use the Website but are required to register as a user if you wish to read the full text of the content and articles available (the Content). You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these terms & conditions or with the prior written consent of Mondaq Ltd. You may not use electronic or other means to extract details or information about Mondaq.com’s content, users or contributors in order to offer them any services or products which compete directly or indirectly with Mondaq Ltd’s services and products.


Mondaq Ltd and/or its respective suppliers make no representations about the suitability of the information contained in the documents and related graphics published on this server for any purpose. All such documents and related graphics are provided "as is" without warranty of any kind. Mondaq Ltd and/or its respective suppliers hereby disclaim all warranties and conditions with regard to this information, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. In no event shall Mondaq Ltd and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of information available from this server.

The documents and related graphics published on this server could include technical inaccuracies or typographical errors. Changes are periodically added to the information herein. Mondaq Ltd and/or its respective suppliers may make improvements and/or changes in the product(s) and/or the program(s) described herein at any time.


Mondaq Ltd requires you to register and provide information that personally identifies you, including what sort of information you are interested in, for three primary purposes:

  • To allow you to personalize the Mondaq websites you are visiting.
  • To enable features such as password reminder, newsletter alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our information providers who provide information free for your use.

Mondaq (and its affiliate sites) do not sell or provide your details to third parties other than information providers. The reason we provide our information providers with this information is so that they can measure the response their articles are receiving and provide you with information about their products and services.

If you do not want us to provide your name and email address you may opt out by clicking here .

If you do not wish to receive any future announcements of products and services offered by Mondaq by clicking here .

Information Collection and Use

We require site users to register with Mondaq (and its affiliate sites) to view the free information on the site. We also collect information from our users at several different points on the websites: this is so that we can customise the sites according to individual usage, provide 'session-aware' functionality, and ensure that content is acquired and developed appropriately. This gives us an overall picture of our user profiles, which in turn shows to our Editorial Contributors the type of person they are reaching by posting articles on Mondaq (and its affiliate sites) – meaning more free content for registered users.

We are only able to provide the material on the Mondaq (and its affiliate sites) site free to site visitors because we can pass on information about the pages that users are viewing and the personal information users provide to us (e.g. email addresses) to reputable contributing firms such as law firms who author those pages. We do not sell or rent information to anyone else other than the authors of those pages, who may change from time to time. Should you wish us not to disclose your details to any of these parties, please tick the box above or tick the box marked "Opt out of Registration Information Disclosure" on the Your Profile page. We and our author organisations may only contact you via email or other means if you allow us to do so. Users can opt out of contact when they register on the site, or send an email to unsubscribe@mondaq.com with “no disclosure” in the subject heading

Mondaq News Alerts

In order to receive Mondaq News Alerts, users have to complete a separate registration form. This is a personalised service where users choose regions and topics of interest and we send it only to those users who have requested it. Users can stop receiving these Alerts by going to the Mondaq News Alerts page and deselecting all interest areas. In the same way users can amend their personal preferences to add or remove subject areas.


A cookie is a small text file written to a user’s hard drive that contains an identifying user number. The cookies do not contain any personal information about users. We use the cookie so users do not have to log in every time they use the service and the cookie will automatically expire if you do not visit the Mondaq website (or its affiliate sites) for 12 months. We also use the cookie to personalise a user's experience of the site (for example to show information specific to a user's region). As the Mondaq sites are fully personalised and cookies are essential to its core technology the site will function unpredictably with browsers that do not support cookies - or where cookies are disabled (in these circumstances we advise you to attempt to locate the information you require elsewhere on the web). However if you are concerned about the presence of a Mondaq cookie on your machine you can also choose to expire the cookie immediately (remove it) by selecting the 'Log Off' menu option as the last thing you do when you use the site.

Some of our business partners may use cookies on our site (for example, advertisers). However, we have no access to or control over these cookies and we are not aware of any at present that do so.

Log Files

We use IP addresses to analyse trends, administer the site, track movement, and gather broad demographic information for aggregate use. IP addresses are not linked to personally identifiable information.


This web site contains links to other sites. Please be aware that Mondaq (or its affiliate sites) are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of these third party sites. This privacy statement applies solely to information collected by this Web site.

Surveys & Contests

From time-to-time our site requests information from users via surveys or contests. Participation in these surveys or contests is completely voluntary and the user therefore has a choice whether or not to disclose any information requested. Information requested may include contact information (such as name and delivery address), and demographic information (such as postcode, age level). Contact information will be used to notify the winners and award prizes. Survey information will be used for purposes of monitoring or improving the functionality of the site.


If a user elects to use our referral service for informing a friend about our site, we ask them for the friend’s name and email address. Mondaq stores this information and may contact the friend to invite them to register with Mondaq, but they will not be contacted more than once. The friend may contact Mondaq to request the removal of this information from our database.


From time to time Mondaq may send you emails promoting Mondaq services including new services. You may opt out of receiving such emails by clicking below.

*** If you do not wish to receive any future announcements of services offered by Mondaq you may opt out by clicking here .


This website takes every reasonable precaution to protect our users’ information. When users submit sensitive information via the website, your information is protected using firewalls and other security technology. If you have any questions about the security at our website, you can send an email to webmaster@mondaq.com.

Correcting/Updating Personal Information

If a user’s personally identifiable information changes (such as postcode), or if a user no longer desires our service, we will endeavour to provide a way to correct, update or remove that user’s personal data provided to us. This can usually be done at the “Your Profile” page or by sending an email to EditorialAdvisor@mondaq.com.

Notification of Changes

If we decide to change our Terms & Conditions or Privacy Policy, we will post those changes on our site so our users are always aware of what information we collect, how we use it, and under what circumstances, if any, we disclose it. If at any point we decide to use personally identifiable information in a manner different from that stated at the time it was collected, we will notify users by way of an email. Users will have a choice as to whether or not we use their information in this different manner. We will use information in accordance with the privacy policy under which the information was collected.

How to contact Mondaq

You can contact us with comments or queries at enquiries@mondaq.com.

If for some reason you believe Mondaq Ltd. has not adhered to these principles, please notify us by e-mail at problems@mondaq.com and we will use commercially reasonable efforts to determine and correct the problem promptly.