Uncle Sam doesn’t e-mail. Period.

Not with offers about free government money that’s yours for the asking. Not about an overlooked tax refund. And not because you won some faraway lottery and U.S. Customs is nice enough to inform you.

Rather, that incoming .gov message is coming from Uncle Sham.

So when you get an electronic message from a government agency—be it the IRS, the FBI, the Social Security Administration or any other tax-supported office—know that it’s fake and more likely to originate from Nigeria than from Washington.

“E-mail scammers are looking for every opportunity to steal your money and personal information,” FBI Special Agent Richard Kolko said in a recent statement. “These criminals are increasingly attempting to do this by falsely claiming to be various government officials.”

Although bogus government e-mails are nothing new, they’re becoming more common. Some 1,500 scams have been committed under the guise of the IRS alone.

In fact, one new scheme targets previous victims of Internet fraud, promising that refunds are available to compensate them for their losses. Claiming to be from the FBI’s Internet Crime Complaint Center, the Metropolitan Police, the government of the United Kingdom and the Bank of England, the e-mail says the refund will be sent via bank wire once a “fund release order” is signed and submitted. But filling out such an order will give the scammers access to your bank account—and nothing but a headache to you. A tip-off that these e-mails are phony: They’re filled with spelling and grammatical errors, suggesting that they’re generated from a foreign country.

Another popular “government” e-mail is one allegedly sent by the IRS. Recipients are told that they can have their economic stimulus rebate checks direct-deposited by providing their bank account numbers on an attached order form. In another, years-old IRS scam that’s still making the rounds, the e-mail says an error has been made on a previous tax return, so the recipient is entitled to a refund of several hundred dollars—of course, it can be direct-deposited.

Kolko’s advice, should you get an e-mail purporting to be from any government agency, whether it’s federal, state or local: “Don’t respond, don’t open the attachments, and don’t send your money or personal information.” Clicking on any attachment or link could unleash dangerous viruses that can steal your identity and hamper your computer’s performance.

Report such e-mails to the FBI’s complaint center. Forward those “sent” by the IRS—unopened—to phishing@irs.gov, an e-mail account.

The FBI and lookstoogoodtobetrue.com provide more information on cyber-crimes. Meanwhile, remember: If Uncle Sam wants to get in touch with you, you’ll get a letter via U.S. mail—not via e-mail.

Sid Kirchheimer is the author ofScam Proof Your Life(AARP Books/Sterling).