Under the joint initiative, Sentinel, the products-focused subsidiary of Sentinel Tech Holding, will build and maintain a monolithic database of the United States' 550,000 registered sex offenders, while MySpace will develop technology for using the information in the database and the profiles of its 130 million users to detect potential predators. In addition, MySpace is advocating a law that would require those found guilty of sex crimes to register all their e-mail addresses with the national database.

"The bottom line is that convicted sex offenders are not welcome on our site," said Hemanshu Nigam, chief security officer for MySpace.

The move comes as MySpace continues to deal with a number of incidents that have undermined the service's reputation as a safe place to hang out online. The broadest impact has been from digital attacks: A variety of scripting programs known as Web worms have used Javascript and cross-site scripting to spread and install malicious software, such as adware, on members' computers.

However, it's the threat of sexual predators preying on MySpace's minors that has the company most worried. In June, a 14-year-old girl and her mother filed suit against News Corp., the owner of MySpace, for failing to protect the girl from a 19-year-old man that contacted her through the site and allegedly attacked her. In October, a Wired News editor used a simple script to mine the national registry of sex offenders and MySpace, finding 744 confirmed offenders with profiles on the service.

MySpace has worked with Sentinel to develop the design of the database, which will use a variety of public and commercial information to create detailed profiles of convicted sex offenders listed in the 46 available state registries. The companies will vet the database for accuracy, said John Cardillo, CEO of Sentinel Tech Holding.

"As these databases exist today, they are a scrape of what's on the public records," Cardillo said. "We are using proprietary data and linking other non-public information with it to create our database, and we are using additional technologies to ensure that we have the right person and we can effectively track them."

While a law requiring that convicted sex offenders register their e-mail addresses with the state registries would help better identify the people online, it's not necessary for Sentinel's database to work, Cardillo said. However, the identity verification company, which also runs online ID check service Sentry, declined to further describe the technology.

"We don't want to say how we do what we do, because we don't want to tip our hands to the people that will use these sites for the wrong reasons," Cardillo said.

MySpace registration and the sex offender registries require some similar information, such as a person's name, date of birth and zip code. It's unclear whether a person that fabricates the information would get caught.

MySpace has high hopes for the technology, which is being called Sentinel Safe.

"The creation of the first-of-a-kind real-time searchable database technology is a significant step to keep our members as safe as possible," MySpace's Nigam said in a statement announcing the initiative. MySpace hired Nigam in April from Microsoft, where he acted as a cybercrime investigator, to help the company secure its service.

MySpace will pair its use of the database with a security team available around the clock to deal with any potential database matches, Nigam said. The deal with Sentinel aims to head off convicted sex offenders from using the service for any reason.

The MySpace initiative will likely reignite a debate over sex offender registries. Citizen rights groups, such as the American Civil Liberties Union (ACLU) have criticized the registries as error-prone and overly inclusive of even minor crimes. A spokesperson for the ACLU on the issue could not immediately be reached.

Moreover, MySpace may have to defend its assessment that anyone convicted of a sex crime should not be allowed on its service. In a 2005 op-ed letter to the CrimProfBlog, Margaret Colgate Love, a twenty-year veteran of the U.S. Department of Justice, criticized the policy of posting such lists online, arguing that they lead to vigilantism.

"I am sure there are sex offenders living in the community who need to be surveilled, and probably some who really should be locked up," the letter stated. "But the clear suggestion that all 500,000 registered sex offenders in the United States are 'predators' is one of the most irresponsible I've seen come out of the Justice Department, ever."

In April, a 24-year-old Maine man was killed by a vigilante, who subsequently killed himself, when his name was taken from that state's list of sexual predators. The victim had been convicted of having sex with a minor when he was 19 years old.

MySpace said the technology will be ready to be deployed in 30 days.