IT contractors seeking employment should beware job-related email spam, an internet security firm has warned.

Taking advantage of higher levels of unemployment, cyber criminals are using emails advertising jobs to distribute a Mabezat worm, according to BitDefender.

Spam emails with titles like 'Web designer vacancy' or 'We are hiring' are hiding the Win32.Worm.Mabezat.J worm in seemingly harmless extractable files.

The Mabezat family of worms are particularly dangerous, as once extracted they collect e-mail address from a variety of file formats, before mass-mailing them, BitDefender claims.

"In order to stay safe, computer users should ensure that they have installed a complete antimalware suite. Never open files from unfamiliar locations,” warned Catalin Cosoi, senior researcher at BitDefender.

What is different about this particular worm is that it can replace the first 1,768 bytes of the infected executable file with its own encrypted body, and it always targets Windows Media Player and Outlook Express files first.

Earlier this week, BitDefender warned that Trojan.AutorunInf.Gen, which spreads via removable devices, is now the most prevalent malware threat, accounting for nine per cent of all global infections.