Cyber security experts have warned that organised hacking gangs are posing as lawful IT companies and are selling malicious software in the disguise of anti-virus software.

These hacking gangs are pocketing millions of pounds by selling fake security software for up to £30. The malicious software helps criminals infiltrate customers' systems and steal their confidential banking details.

The stolen information is then combined with credit card details acquired from the sale to swindle the customer. Gangs are targeting customers using direct telephone calls.

The Serious & Organised Crime Agency's Sharon Lemon, who shoulders the responsibility for fighting back cyber crime, described hacking gangs' this trick as big business.

Speaking on the issue, Lemon said, "In recent cases, we have seen gangs employing 300 to 400 people to run their operations and using call centre-scale set ups to target victims en masse."

Thousands of users in the UK are receiving spam e-mails offering virus check services, while 48 per cent of all web users are seeing a pop-up window claiming their computers are infected. Around 25 per cent of web users have already been contacted by someone claiming to be from an IT helpdesk.