More than 5 percent of Internet address names issued in the United States are registered using "patently false" contact information, making it difficult or impossible to contact the sites' owners, according to report submitted to Congress.

Another 3.7 percent of domain names ending in ".com," ".net" and ".org" contain missing information in required contact fields, the Government Accountability Office said in a report submitted to the House Subcommittee on Courts, the Internet and Intellectual Property.

In all, 3.9 million names, or about 8.7 percent, contain contact details that "appeared obviously and intentionally false" or are incomplete, the report said.

Under rules enforced by the Internet Corporation for Assigned Names and Numbers, which has oversight over the Net's addressing system, registrars must collect phone numbers, physical mailing addresses and other contact information from domain name owners.

That information is made public to help individuals, businesses and law enforcement contact Web site operators to answer questions, resolve disputes and troubleshoot network problems.

But in recent years the databases have been mined by telephone marketers and people sending unsolicited e-mail and postal mail, causing some Web site owners to falsify or withhold addresses and phone numbers, observers said.

"The incentive to provide correct information has certainly gone down," said Carl Malamud, chief technology officer for the Center for American Progress.

ICANN requires domain name registrars to investigate and correct any reported inaccuracies in contact information, and the registrars have the right to cancel a domain name for incorrect data.

However, of 45 owners with incorrect information reported to ICANN, 33 remained uncorrected 30 days later, the report said.