IT contractors have been warned that social networking sites are becoming increasingly important tools for cyber criminals.

Many corporate security systems do not scan social networking vectors for malicious threats, according to IT security firm Sophos.

In addition, users are much more likely to open emails seemingly sent from friends' Facebook profiles than a typical spam email, when this account could easily have been hacked.

"Sophos surveyed over 500 organisations, and discovered that 72 per cent are concerned that employee behaviour on social networking sites exposes their businesses to danger," said Graham Cluley, senior technology consultant for Sophos.

It is therefore vital that security systems scan every link or webpage that is accessed, while users must be urged to use complex non-dictionary passwords, Mr Cluley adds.

Research from Sophos, published earlier this year, found that malware and spam from social networks has increased by 70 per cent in the last 12 months.