Privacy experts have long said that even anonymous Web users sometimes leave behind enough clues that people can piece together their identities.
Already there have been a few famous occurrences. In 2006, after AOL released search logs showing queries made by more than 650,000 "anonymized" members, The New York Times was able to find and profile one of them within days. Several years later, when Netflix released some data for a contest, two University of Texas computer scientists reported that it was possible to identify users by comparing reviews of obscure movies on Netflix with reviews on Imdb.com that were published under screennames.
Now a federal prosecutor in New Orleans has been identified based on his Web posts. Assistant U.S. Attorney Sal Perricone in New Orleans was just unmasked as the NOLA.com commenter "Henry L. Mencken1951."
In the last six months, "Mencken" left almost 600 comments at the Times-Picayune's NOLA.com . Many of the posts showed detailed knowledge about the prosecutor's office and judicial proceedings -- including a pending investigation centered on the local River Birch landfill, which is co-owned by Fred Heebe.
Heebe himself hasn't been charged with any crimes, but another executive at the landfill is facing charges.
Heebe this week filed a defamation lawsuit against Mencken for posts that allegedly included "false and defamatory accusations." As part of that lawsuit, Heebe sought to take depositions from Perricone as well as a second federal prosecutor.
Heebe said in his court papers that he suspected that Mencken was Perricone, based on a report by former FBI profiler James Fitzgerald -- hired by Heebe to study the comments and determine the author's name.
Fitzgerald concluded that Mencken1951 was a prosecutor by comparing Mencken's posts with legal papers filed by a team that included Perricone. The biggest similarities were in word choices; Mencken's posts and the prosecutors' legal papers included the long out-of-fashion words "dubiety" and "redoubt." Also, Mencken and the prosecutors favored alliteration. The prosecution papers included the phrase "progenitors, progeny and prongs," while the Mencken posts included phrases like, "your fabulous fabulist is finished."
Perricone was also born in 1951, which could explain the 1951 at the end of the Mencken's screenname, Heebe said in his court papers.
Beyond that, the posts themselves showed an intricate knowledge of the government's investigation of the landfill. "Mencken's interest in and level of knowledge about an ongoing ... investigation of River Birch are striking and beyond what could be expected of even the most diligent Times-Picayune reader," Heebe alleged.
Heebe filed his papers on Monday. By Thursday afternoon, Perricone had confirmed he was the commenter.