There are three “rats of the week” on the home page of whosarat.com, a Web site devoted to exposing the identities of witnesses cooperating with the government. The site posts their names and mug shots, along with court documents detailing what they have agreed to do in exchange for lenient sentences.

Last week, for instance, the site featured a Florida man who agreed in September to plead guilty to cocaine possession but not gun charges in exchange for his commitment to work “in an undercover role to contact and negotiate with sources of controlled substances.” The site says it has identified 4,300 informers and 400 undercover agents, many of them from documents obtained from court files available on the Internet.

“The reality is this,” said a spokesman for the site, who identified himself as Anthony Capone. “Everybody has a choice in life about what they want to do for a living. Nobody likes a tattletale.”

Federal prosecutors are furious, and the Justice Department has begun urging the federal courts to make fundamental changes in public access to electronic court files by removing all plea agreements from them — whether involving cooperating witnesses or not.