Internet users are being threatened by yet another variant of the MyDoom mass mailing worm, which is spreading in part by using email addresses found through popular search engines, security experts warned.
The new variant was first spotted earlier this week and reports from computer users suggest the worm is already circling the globe, according to Graham Cluley, senior technology consultant at antivirus firm Sophos.
The worm proliferates by emailing itself through its own SMTP (Simple Mail Transfer Protocol) engine, according to Sophos. When it infects a computer it scans the hard disk for email addresses and then takes the domains of the addresses it finds and queries search engines such as Google, Yahoo and Lycos looking for similar addresses, Cluley says.
If it finds the address JohnDoe@yahoo.com, for instance, it will use a search engine to look for other addresses at the yahoo.com domain to send itself to, Cluley explained.
A similar MyDoom variant appeared last July and managed to slow some search engines as it flooded them with queries. Cluley said he doubts the new variant will have the same effect since this outbreak is not as severe. Additionally, search engines have taken measures to prevent being crippled by the worm again, Cluley says.
The latest worm was created by repackaging an older MyDoom variant in an encrypted "wrapper" so that antivirus software could not recognise it, Cluley says. The method is just one of the clever ways hackers use to hide their attacks and antivirus firms should be aware of the ruse, he added.
Internet users should make sure their antivirus software is up to date to avoid infection.