Security researchers have reported a new phishing scam targeting users of the U.S. Department of Treasury's Electronic Federal Tax Payment System (EFTPS).

According to McAfee, phishers were seen using the free tax payment service as bait this week in a new round of e-mails.

The e-mails have the subject line "Your EFTPS Tax Payment ID has been rejected," and claim that the recipient's tax payment did not go through due to an invalid ID number. Victims are then directed to a phony Website for more information.

"If you receive one of these messages claiming to be from the EFTPS or IRS, don't open it or click any link," blogged McAfee's Felix Martinez. "It's safer to manually type the URL (web address) instead of clicking a link. To verify whether a government or financial institution is trying to contact you, call that agency."