The FBI says emails made to look like they come from the agency are warning computer users that the FBI is monitoring their internet use.
"These scam emails tell the recipients that their internet use has been monitored by the FBI and that they have accessed illegal websites," the FBI said in a statement. "The emails then direct recipients to open an attachment and answer questions."
"These emails did not come from the FBI," the statement said. "Recipients of this or similar solicitations should know that the FBI does not engage in the practice of sending unsolicited e-mails to the public in this manner."
Opening email attachments from an unknown sender is risky, the FBI said, because such attachments can contain viruses that infect the recipient's computer.
The agency said it was investigating the matter and urged anyone who received such an email to report it to the Internet Crime Complaint Center.