Around one in five companies has had problems with employees misusing the Internet, according to the 2004 Department of Trade and Industry biennial Information Security Breaches Survey in Britain.
There was an average of one incident a week last year in companies reporting a problem - with nearly two-thirds of large companies affected, research findings have shown. The two biggest areas of misuse were excessive personal e-mails and access to inappropriate websites.
Employees had access to the web in 89 per cent of British businesses - 98 per cent in large companies - up from 69 per cent in 2002 when the survey was last carried out, the research said.
Investigations into incidents of misuse lasted typically up to a week, according to the findings.
Mr Chris Potter, of PricewaterhouseCoopers, which led the survey, said: "As more businesses provide their staff with access to the Internet, the number of incidents of staff abusing that access is rising."