The worm spreads via email - forwarding itself to email addresses found on the hard drives of infected computers - and Windows network shares.
When forwarding itself, the worm spoofs the 'From:' field to trick unsuspecting computer users into running the malicious code. Infected emails arrive with a variety of different subject lines and message texts. An attached file has a double extension.
The worm chooses from a selection of filenames when copying itself to shared folders. These names vary from 'angels.pif', 'dictionary.doc.exe' and 'programming basics.doc.exe' to 'sex sex sex sex.doc.exe' and 'hardcore porn.jpg.exe'.
"Worms like this, which don't just rely on email to spread, underline the need for anti-virus protection on the desktop - computer users shouldn't just be relying on email scanning for protection," said Carole Theriault, security consultant, Sophos. "Netsky-B is tricky to identify because of the wide variety of subject lines and message texts, but blocking all files with double extensions is an easy way to avoid infection."