'Sobig.F' Fastest Spreading Computer Virus Ever

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A virus that debuted this week has been declared the fastest spreading e-mail plague of all time, while another malicious program that hit last week continued to disrupt computers worldwide.

MessageLabs Inc., a company that filters e-mail for corporate clients around the world, Wednesday said it had intercepted more than a million copies of the "Sobig.F (search)" virus the previous day, the most it has ever intercepted in a single day. That 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 (search)," at its peak accounted for one in 125 messages scanned.

Sobig.F continued to spread aggressively on Wednesday, though the pace eased off a bit to about one in 60 messages, he said.

The virus, which is the sixth and latest strain of a virus that first emerged in January, spreads through Windows PCs via e-mail and corporate networks.

Besides clogging e-mail systems with messages carrying subject lines like "Re: Details" and "Re: Wicked screensaver," the virus also deposits a Trojan horse, or hacker back door, that can be used to turn victims' PCs into relayers of spam e-mail.

"It's a seeding," Czarny said. "All they're looking to do is plant that Trojan."

Another virus, of the self-spreading kind called a "worm," first appeared last week and was still causing problems Wednesday.

The worm, dubbed "Blaster (search)," spreads through Internet connections to PCs using versions of Microsoft Corp.'s Windows operating system that haven't been fixed for a programming flaw. Microsoft disclosed the error, and provided a patch, on July 16.

Blaster was followed this week by the derivative "Nachi (search)" or "Welchia," which attempts to inoculate computers by downloading the patch from Microsoft. However, the new worm is causing more problems than Blaster, and brought down Air Canada's ticketing systems Tuesday.

Railway giant CSX Corp. said a "worm virus" brought down its signaling systems early Wednesday morning, causing delays and canceled trains through the Eastern states.

Andy Ellis, chief security architect at Web services company Akamai Technologies Inc. said "Nachi" may not be more widespread than Blaster, but it is technically superior and is now generating twice as much Internet traffic as Blaster.

A lot of companies have been reporting problems inside their networks, he said, and there have been "a couple of points where parts of the backbone had performance issues" in the last 24 hours.

"Nachi is a long-term problem that has to be dealt with. These systems absolutely have to be patched," Ellis said.