A new version of the Stration worm has been engineered to infect computers by posing as a computer update, a security vendor has warned.
Sophos said that its latest reports showed that Stratio-AN is "rapidly spreading".
"The Stratio-AN worm has been aggressively distributed by its author since the early hours of Monday morning," said the firm in a statement.
"It spreads via email using a variety of disguises, including an example which ironically poses as a warning that the recipient's computer is infected by a worm."
One version of Stratio-AN uses the email subject line 'Mail server report' and warns users that their PC is sending out emails containing the worm.
The bogus customer support service email contains a zipped file with the name 'Update-KB7859-x86.zip', which installs the worm on the user's PC.
"This new offspring of Stration is hitting email gateways hard, attempting to infect unsuspecting computer users," said Graham Cluley, senior technology consultant at Sophos.
"Anyone accessing their email has to learn to resist the temptation of opening unsolicited attachments, and ensure that their anti-malware protection is kept fully up to date."
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