The Federal Bureau of Investigation issued an alert Monday about a scam involving unsolicited e-mails, purportedly sent by the FBI, that tell computer users that their Internet surfing is being monitored by the agency.

The users are told they have visited illegal Web sites and are instructed to open an attachment to answer questions.

The FBI did not send these e-mails and does not send any other unsolicited e-mails to the public, an agency statement said. As many harmful computer viruses are located in e-mail attachments, the FBI said it strongly encourages computer users not to open attachments from unknown recipients.

The FBI is investigating the scam. Recipients of these e-mails are asked to report them by visiting the Internet Crime Complaint Center at http://www.ic3.gov.