IT contractors are being urged to check flash drives, memory cards and external hard disks for malware on a regular basis by a leading security company.

According to the latest report from BitDefender on the most prevalent e-threats, Trojan.AutorunInf.Gen features at the top of the list.

The generic mechanism spreads via removable devices and is now responsible for the most infections of malware, at nine per cent of total global cases.

IT contractors using unchecked portable devices for different clients could be unwittingly transferring the infection to their employers.

"External devices should be scanned on a regular basis, especially when these devices have been plugged into public locations that are known to be likely sources of infection," said Catalin Cosoi, BitDefender's senior researcher.

Any IT contractors wanting know more about the changing world of information security can do so at the Infosecurity Europe conference, held at London's Earls Court from April 27th to 29th.

Security professionals will discuss the challenges of tomorrow at the event, which is free if registering before April 23rd.