"These scam e-mails tell the recipients that their Internet use has been monitored by the FBI and that they have accessed illegal websites," the law enforcement agency said in a statement.

"The e-mails then direct recipients to open an attachment and answer questions."

The FBI statement said recipients of this or similar messages "should know that the FBI does not engage in the practice of sending unsolicited e-mails to the public in this manner."

The messages appear to be sent from an e-mail address such as mailAfbi.gov, postAfbi.gov, adminAfbi.gov or a similar address.

The Internet security firm Sophos said similar e-mails may appear to come from the Central Intelligence Agency, but it noted that both contain a strain of the Sober virus that has been spreading worldwide.

In a four-hour period Tuesday, the worm "has accounted for over 61 percent of all viruses reported to Sophos, making it currently the most prevalent virus spreading across the world."

Intellpuke: "This article was posted at BREITBART.com today and I thank them for helping get the word out so we can all watch out for these virus-containing e-mails. I got hit with the one allegedly from the CIA today and yesterday, but had sense enough to kill it out. I figured the CIA and FBI already knows where I am and, if they have questions, they can just call. My Norton Anti-virus has also eliminated about a dozen other e-mails containing the Sober virus in the past two days alone. So be sure to your anti-virus protection is updated.

You can read the BREITBART.com article in context here.