The "Sobig.F" computer virus that began attacking e-mail systems globally Tuesday has been declared the fastest-spreading e-mail virus of all time, according to a report.

WHAT IS IT? How Viruses, Worms Work VIRUS PROTECTION Virus removal tool | Netsky removal Microsoft patch GENERAL PROTECTION Sign Up For Cyber Alerts Download Virus Definitions Other Virus Removal Tools Securities Update Vault REMEMBER: Don't open e-mail attachments that end in .vbs, .pif or other unfamiliar extensions. Even if the e-mail appears to come from a trusted source, it could be someone "spoofing" an address. Confirm it's from who you think it's from before you open.

Meanwhile, the Blaster and Nachi Internet worms continued to bombard corporate networks, having even caused slowdowns on parts of the Internet backbone.

SURVEY How is the SoBig.F virus affecting you? My inbox is hopelessly flooded. My filters are making it easier. I've seen a few odd messages. It's not affecting me at all. Results  |  Disclaimer

MessageLabs Inc., a company that filters e-mail for corporate clients around the world, said it intercepted more than one million copies of Sobig.F Tuesday, the most ever in a single day, according to a Dow Jones report.

The interception rate was one in every 17 e-mail messages the firm scanned. " That's just a number we've never seen before," said Brian Czarny, MessageLabs' marketing director. The most widespread virus of all time, Klez, at its peak accounted for one in 125 messages scanned.

Sobig.F drops software onto infected Windows computers that open them to be used later for distributing Internet spam -- unwanted e-mails and product promotions, experts said. It also represents a new trend in converging e-mail spamming and virus software writing, they said.

"We believe (Sobig.F) has been written by a spammer or spammers" looking for ways to get past spam filters, said Mikko Hypponen, manager of anti-virus research for Finnish security firm F-Secure. "For once, we have a clear motive for a virus -- money."

Security experts said it was difficult to ascertain how many computers had been infected by the Sobig.F worm. Worms are viruses that spread through networks.

Sobig.F hit the computing world as corporations were still recovering from several worms that spread through holes in Microsoft Corp.'s Windows operating systems, including the "Blaster" worm. Also called "LovSan," it has infected and crashed hundreds of thousands of computers since last week.

The "Welchia" or "Nachi" worm, which surfaced on Monday, infected 72,000 computers used by the U.S. Navy and Marine Corps and crippled Air Canada's reservation counters and call centers.

CSX Transportation said on Wednesday that a virus infection had slowed its dispatching and signal systems, forcing it to halt passenger and freight train traffic, including the morning commuter train service in Washington, D.C.

The worm is set to expire Sept. 10, but don't wait until then to delete it. Symantec has a program that you can download to remove SoBig, which lists itself on a computer as winppr32.exe.

Meanwhile, the "good" worm sent to destroy the Blaster or LoveSan virus also caused problems Tuesday. The Welchia worm that appears to be a friend to computers disabled by last week's Blaster virus caused problems for Air Canada passengers Tuesday.

They had to stand in long lines at Canadian airports. The airline had to manually check in passengers after the virus crippled its computers.

Welchia looks for computers infected with the Blaster worm. Then it appears to do the computer a favor by downloading a patch from the Microsoft update site, installing it and rebooting the computer. But then, Welchia begins checking the computer's addresses for other computers on its network to infect by sending "pings" or echos -- swamping networks with activity.

Symantec, an Internet security company, has designated the worm a "level four" threat -- the second-highest.

The original worm only affects computers running Microsoft's Windows XP, Windows 2000, Windows Server 2003 and Windows NT 4.0 operating systems.

Last week, Symantec developed a tool to clean a computer that has been infected by the original worm. You can also use these step-by-step instructions to remove the virus.

How Are Viruses Affecting You?