While three-quarters of users are worried about viruses, ten percent do not bother to update their antivirus software, according to research by LloydsTSB.
The survey of 1,400 people revealed the various reasons cited by users for failing to keep antivirus software updated. 13 percent thought antivirus software was too expensive, eight percent didn't know it was necessary and six percent said "I can't be bothered".
A further five percent didn't know if they have antivirus software installed on their PC. The survey found that virtually all respondents (94 percent) thought it important to regularly update their antivirus software.
In response to the survey findings, the bank is offing users a free security scan of their computers from Zone Labs, although users will have to use Internet Explorer with ActiveX enabled to use the service.
Matthew Timms, internet banking director of Lloyds TSB, said many home banking users didn't keep their antivirus software up to date or bother installing it, even though they knew it was important to do so.
"The impact of a computer virus can be extensive and in some cases result in a compromise of PC security," said Timms.