Most Americans believe their computers are protected against viruses and spyware, but scans found that a large number had outdated or disabled security software, according to a poll released on Monday.

Fully 87 percent of Americans polled said they had anti- virus software, 73 percent said they had a firewall and 70 percent said they had anti-spyware software, according to the survey by security software maker McAfee Inc (MFE) and the National Cyber Security Alliance.

But when pollsters asked to remotely scan the respondents' computers, the story turned out to be very different.

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While 94 percent of those polled had anti-virus software, just half had updated it in the past month, the survey showed. Eighty one percent had a firewall protecting private information, but just 64 percent had enabled it. And 70 percent said they had anti-spyware software, but only 55 percent had enabled it.

Spyware not only monitors what a computer user does, but can also install software without the user's consent and interfere with the computer in other ways.

Bari Abdul, a McAfee vice president, said most viruses were not written by attention-seeking hackers looking to pull a prank.

"Most of the action has gone to stealing identity," he said after speaking at a cyber security conference sponsored by the National Cyber Security Alliance.

Nine percent of those polled reported having had their identity stolen, he said.

The survey questioned 378 people between Aug 2 and Sept 10 about security on their home computers. The Cyber Security Industry Alliance is seeking U.S. legislation to set standards for the government and private industry to prevent data breaches and tougher criminal penalties against spyware.

The Federal Trade Commission, which is one of several government agencies investigating cyber fraud, said on Monday it had stopped a scam that had infected 15 million computers.

Three men, who gave up the $330,000 they made from the scam, collected various forms of spyware and adware and used them to infect computers, the FTC said. They made money by putting adult ads on the computers and advertisements for Internet-based businesses or travel.

The unwanted software was hidden in free screen-savers and video files that users downloaded.

"Every time they infect a consumer, they're getting paid," said Ethan Arenson, one of the FTC lawyers who worked on the case.

FTC Chairman Deborah Majoras urged computer users to protect themselves against malicious software.

"I can tell you we have two dozen open investigations into data security," said Majoras. "We can't round up all the bad guys."

Majoras said she wanted to computer users to hit "delete" instead of "reply" when they get spam or email which is "phishing" for personal information that could be used for identity theft.

"Phishing absolutely drives me insane," she added.