Another variant of the MyDoom worm, which spreads by sending copies of itself using its own mail engine and harvesting potential e-mail targets from search engines such as Google and Yahoo, was spreading quickly on Thursday.

Last summer, a MyDoom variant pumped so many queries into Google that the search engine was unavailable or very slow for large periods of time. The same variant of MyDoom also succeeded in knocking a number of smaller search engines--including Lycos and Altavista--off the Web completely.

Antivirus firm Sophos said the latest MyDoom variant searches an infected computer's hard disk for e-mail addresses and then reverts to an Internet search. Interestingly, the worm tries to search the Internet for e-mail addresses in the infected computer's domain--effectively targeting all users from a specific company or service provider.

According to a Sophos advisory, the worm "will send a query to the search engine using domain names from e-mail addresses found on the hard disk and then examine the query results, searching for more addresses."

Sean Richmond, senior technical consultant at Sophos in Australia and New Zealand, said that the latest variant was first detected early Thursday and that as long as people have updated their virus definitions it shouldn’t cause much of a problem.

"We saw a spate of samples come through over the last day into our lab. By now a lot of companies are already blocking dodgy zip files and quite a few of the infected e-mails are automatically blocked as spam. It is spreading but everyone (including alternative antivirus companies) are on top of things," Richmond said.

Sophos said the worm will send 45 percent of its queries to Google, 22.5 percent to Lycos, 20 percent to Yahoo and 12.5 percent to Altavista.

Antivirus firms Sophos, Computer Associates and Symantec all agree that the worm is spreading quickly but is relatively simple to remove using their latest antivirus definitions.

So now is it harmful to us? I mean home users. If yes what does it do? I hope the firewall will help. Any ideas?