Around a tenth of all malware is designed to use portable storage media, such as removable USB drives, as an attack and spread vector.

Security firm ESET said that 10.3 per cent of malware detections last month were identified as files containing information on programs to be run automatically when removable media are inserted into a computer.

ESET revealed that INF/Autorun, a generic identification for malware that tries to use the autorun.inf file as a way of compromising a PC, has retained its number one spot and increased its share of detected malware during March.

"Portable storage media started to become a noticeable threat last summer," said Paul Brook, managing director of ESET UK.

"Since then it has gathered pace and continues to grow as a popular infection vector with malware writers, and it is easy to see why.

"It has been drummed into users for so long that email is the main source of infection that users have forgotten the threats from yesteryear when media such as floppy disks were the main concern.

"Consequently, basic desktop protection is now often overlooked, particularly by home users."

Adware still features prominently in the top 10 detected threats in March, with variations of the pernicious Virtumonde steadfastly refusing to budge.

Virtumonde is causing misery to computer users that have had their machines compromised because of inadequate protection.

"Some PC users report instances where this program has taken over a system to such an extent, displaying so many unwanted advertising windows, that the PC becomes all but unusable," said Brook.

"The problem is exacerbated by the fact that if the malware is not fully removed, it will try to replace registry keys and malicious DLLs. There are generic tools available that can help, but they need some knowledge to use safely."