On 9 March 2016, the Provincial Court Düsseldorf ("LG Düsseldorf") held that using Facebook's popular Like-Button on a business website contravenes privacy and unfair competition laws if the users are not properly informed and thus did not give their consent to the respective data use (.pdf-download-link: LG Düsseldorf, Docket No. 12 O 151/15 [only available in German language]):
"Using the Facebook-"Like"-Plugin on the Defendant's website without informing the users about the transfer of their IP address and their browser-string to Facebook prior to that transfer is unfair under sec. 3a of the [German] Unfair Competition Act in conjunction with sec. 13 of the [German] Telemedia Act."
In Austria, using the Like-Button without proper information to the users may equally breach the Austrian Data Protection Act. Whether this breach automatically also is "unfair" under the Austrian Unfair Competition Act, however, may be questioned.
Ultimately, the crucial question remains whether IP addresses are to be qualified as personal data in general: Although the Internet and the privacy laws have been around for ages, this question was referred to the European Court of Justice yet on 17 December 2014 for the very first time (ECJ, C-582/14). It will certainly take some time until the ECJ finally resolves this question. Hence, this strikingly shows the differences in the pace of the technological and the legal developments.
Until then, businesses should strive after using alternatives which may provide as much legal certainty as possible: E.g., the renowned professional journal c't claimed to have developed a privacy-friendly Open Source alternative called "Shariff" for implementing various Social Media Buttons (see c't Link [only available in German language]).
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.