Editor's note:We first posted the story in June 2014. Beginning in November 2015, we've started getting lots of calls saying that the scam is resurfacing, so we're re-posting this story as a reminder.

DENVER - Denver is the target of a sophisticated IRS scam in which thieves posing as IRS agents threaten to arrest taxpayers for not paying back taxes.

It's all done over the phone and is very convincing. The thieves even called 9NEWS Reporter Mark Koebrich and tried to extort some $2,000.

It starts with a very threatening phone call from a thief purporting to be with the Treasury Department. You are told there is a warrant out for your arrest for failure to pay back taxes. The debt is payable immediately, or you are subject to arrest at your workplace, and off to jail for six months.

You are told you need to leave work or home while you are on the phone, and go and purchase a special IRS voucher without delay. You are never allowed to the hang the phone up, or, the thieves tell you they will send officers to take you into custody immediately.

Typically, the thieves direct you to a local grocery store where you purchase the so called "voucher," which turns out to be nothing more than a prepaid card. The thieves say they will cash the card to satisfy the tax debt and stop the warrant that has been issued for your incarceration.

9NEWS followed the scheme to the end and had we not been aware, we would have paid as thousands of others have. About 10 percent have been caught in the scheme and lost money.

(KUSA-TV © 2014 Multimedia Holdings Corporation)