Hackers are spreading a vicious computer virus through spam email messages that urge recipients to visit a bogus website offering vaccinations to protect them against another virus -- the one that causes swine flu.

The email purports to be from the U.S. Centers for Disease Control, directing them to what looks like an official government website to fill out a vaccination form, said researchers from security firms Symantec Corp and AppRiver.

Security researchers said they began seeing millions of spam messages on Tuesday as part of a scheme to infect computers with malicious software that lets hackers take control of computers.

The hacker-controlled site then automatically downloads malicious software onto a victim's PC.

Once in control of the computer, the hackers can use a compromised machine to commit identity theft, attack other computers or turn the PC into a spam server.

Hackers typically base scams on issues that are at the top of the news. In recent days they have launched attacks linked to Tiger Woods' car crash and the kickoff of the annual holiday shopping season.

(Reporting by Jim Finkle; Editing Bernard Orr)

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