Internet users are being warned about cold callers who offer to fix viruses but then install software to steal personal information.
Campaign group Get Safe Online said a quarter of people it had questioned had received such calls, many suspected to have been from organised crime gangs.
Some gangs, employing up to 400 people, are known to set up their own call centres to target people en masse.
Internet users are also urged to be wary of pop-ups offering virus checks.
Earlier this year, search engine giant Google warned it had discovered massive amounts of malicious fake anti-virus software.
Read More/Source: BBC News