The Web site www.whosarat.com promotes itself as the "largest online database of informants and agents," listing 4,727 profiles of "rats" -- 426 of whom are purportedly of undercover law enforcement agents.
The information, submitted by users "may not be 100 percent accurate and should be used for information/entertainment purposes only," according to the site.
But the Department of Justice isn't amused.
"Witnesses are the lifeblood of the work of the Department of Justice," said Associate Deputy Attorney General Ronald Tenpas.
"And anything that makes people fearful that coming forward and providing information is something that's of great concern to us."
The purpose of the site, it says, is to compile a database of informants, designed to assist attorneys and defendants in their research.
The site's disclaimer states: "The information contained within is definitely not an attempt to intimidate or harass informants or agents or to obstruct justice. This Web site's purpose is for defendants with few resources to investigate, gather and share information about a witness or law enforcement officer."
'It's Kind of on Them'
The government's concern, however, stems from cases such as that of a Philadelphia drug courier, who was arrested and agreed to testify against one of his associates. Shortly thereafter, fliers with information on the man available at the Who's a Rat site, including his photo, appeared in his neighborhood on utility poles, cars and in the mail.
"That situation got so serious we had to relocate the witness, we were so concerned about the witness' safety," said Tenpas.
"The solution is not to scare witnesses so they won't come forward and won't tell their stories at all, and that's what this appears to be about... preventing people from stepping forward because they're afraid the next thing that'll happen is there'll be posters up in their neighborhood labeling them a rat or a snitch," he said.
"If people got hurt or killed, it's kind of on them. They knew the dangers of becoming an informant," a site spokesman identifying himself as Anthony Capone told the Associated Press in November 2006.
Capone continued, "We'd feel bad, don't get me wrong, but things happen to people. If they decide to become an informant, with or without the Web site, that's a possibility."
Capone is listed as the administrative and technical contact for the site, which is registered in the name of Sean Bucci, according to domain name registration information available via www.whois.com.
A Massachusetts' jury convicted Bucci in February on federal drug, money laundering and tax evasion charges. He is currently in federal custody, awaiting sentencing next month. Bucci could face life behind bars and fines of up to $4 million.
In court documents related to Bucci's trial, the prosecution noted "his defense was that he was the victim of a vast government conspiracy in which the prosecutor persuaded all the cooperating witnesses to lie to the Jury."
Those "cooperating witnesses" -- or informants -- were reportedly Bucci's reason for starting the site in 2004.
'The Rise of a New Cottage Industry'
The Department of Justice is not aware of any cases in which a person appearing on the site had been hurt as a result of the publicity, but the department has had its eye on the site, as it said witnesses have been threatened and intimidated after their profiles surfaced on the site.
The former head of the Executive Office for U.S. Attorneys, Mike Battle, referred to it in a December 2006 letter to the U.S. Judicial Conference, the main policymaking organization for the U.S. courts system.
"We are witnessing the rise of a new cottage industry engaged in republishing court filings about cooperators on Web sites such as www.whosarat.com for the clear purpose of witness intimidation, retaliation and harassment," Battle wrote.
Battle's letter outlined some steps the courts could take to combat the "increased threat to cooperating witnesses and defendants" potentially seen by sites like Who's a Rat, including removing plea agreement documents from Pacer, the federal government's online court document system, posting a warning to users against posting the documents for illicit purposes on the Pacer login screen, and creating a nationwide policy for courthouses, allowing them to restrict use of cell phones and other recording devices.
"The posting of photographs of cooperating witnesses on Web sites such as 'whosarat' has greatly exacerbated the concern that cooperators will be publicly identified, stigmatized and harmed," the letter said.
Tenpas said the guidelines being discussed are not an attempt to close off court documents and trials to the public, because the information would still be available, just not as easily to someone "who really doesn't care for any reason other than harassment and embarrassing witnesses."
Freedom of Speech
But the site contends it's protected under the law: "Freedom of speech, freedom of information act, and an individual's constitutional right to investigate his or her case protect this Web site."
Tenpas countered: "There are appropriate First Amendment concerns here, but whether there's a First Amendment right or not, it's not a responsible thing to be posting on an Internet site the names and identities undercover law enforcement agents."
He continued: "Somebody can protect their interest in getting a fair trial and having a level playing field by going to trial, cross-examining those witnesses, have a judge oversee all of that to make sure the government is putting on a fair and full case."
E-mails sent to contact e-mail addresses listed on the site apparently forwarded to Bucci's personal AOL account, also listed with the site's registration information.
An error message reply indicated the AOL mailbox is full. ABC News contacted a site spokesman through an additional e-mail address. Chris Brown responded saying he would answer questions, but did not reply to follow up e-mails attempting to arrange an interview.
ABC News' Cindy Smith contributed to this report.