Computer scientists Arvind Narayanan and Dr Vitaly Shmatikov, from the University of Texas at Austin, developed the algorithm which turned the anonymous data back into names and addresses.
The data sets are usually stripped of personally identifiable information, such as names, before it is sold to marketing companies or researchers keen to plumb it for useful information.
Before now, it was thought sufficient to remove this data to make sure that the true identities of subjects could not be reconstructed.
The algorithm developed by the pair looks at relationships between all the members of a social network -- not just the immediate friends that members of these sites connect to.
Social graphs from Twitter, Flickr and Live Journal were used in the research.
The pair found that one third of those who are on both Flickr and Twitter can be identified from the completely anonymous Twitter graph. This is despite the fact that the overlap of members between the two services is thought to be about 15%.
The researchers suggest that as social network sites become more heavily used, then people will find it increasingly difficult to maintain a veil of anonymity.
If it's privacy you're after, just stay off the freakin' Internet.