Linking to a website that contains copyright infringing content does not constitute a violation of the copyright law, according to European Court of Justice's Advocate General. While his opinion is not binding, it's usually followed by the court.
According to the Advocate General, "hyperlinks placed on a website greatly facilitate the discovery of other websites, and protected works available on those sites, and as a result offer users of the first website faster and more direct access to those works".
However, the Advocate General clearly makes a difference (PDF) between making content available and facilitating discovery of content. According to him, "hyperlinks which lead, even directly, to protected works are not 'making them available' to the public when they are already freely accessible on another website, and only serve to facilitate their discovery."
Instead, he added, the "actual making available of the content is is the action of the person who effected the initial communication" and the initial communication should have been authorized by the copyright holder. Thus, linking to copyrighted content is not a copyright violation and publishing copyrighted content without the copyrights owner's consent, obviously, is.
The case arose in the Netherlands where the website GeenStijl linked to a site showing pictures of a Dutch celebrity taken by Playboy magazine. The site hosting the pictures did not have Playboy's consent to do so.
