If an unexpected windfall from the IRS lands in your bank account before Tax Day, don’t count yourself lucky. It’s not a convenient new tax break, but a scam by identity theft experts hoping to collect fraudulent tax refunds.

Here’s how it works, according to WIRED: First, you’ll notice a sudden influx of cash in your bank account courtesy of the IRS. Clearly, the deposit is a mistake—you haven’t even started filing your taxes yet. But it’s not a clerical error. Someone has stolen your identity and filed taxes on your behalf, eager to reap the rewards from the IRS. Soon after the funds are deposited, you’ll get a call demanding the money back. A scammer will pose as someone from a collection agency linked with the IRS, demanding the money back. In some cases, people receive robocalls saying they could be arrested if they don’t return the money ASAP—to the scammers’ “collection agency,” that is.

It’s a clever scheme because the money is, in fact, in your account, and since you know it isn’t the refund you filed for, it’s easy to convince you that you need to give the money back. But obviously, you don’t want to send it to your scammer.

The IRS has issued several warnings about the scam, asking financial professionals to watch out for phishing attacks and, in general, to beef up their security procedures. The agency traced the scam back to hackers stealing data from the computers of tax professionals, giving them access to the personal information necessary to file fraudulent tax returns.

Since the 2018 tax deadline isn’t until April 17, it’s safe to say that most of us haven’t filed our taxes yet. So if you do see a few thousand dollars (or up to $20,000, according to The New York Times) waltz into your account from the government, it probably isn’t legit. Here’s what to do if you fall victim to it:

Report your identity as stolen. You’ll need to file a complaint at identitytheft.gov. The site will help guide you through the process and provide you with the forms you need.

If you’ve received a direct deposit, contact your bank and have them return it. You’ll need to go through the bank’s Automated Clearing House (ACH) department. Then call the IRS at 1-800-829-1040 to tell them what happened and why they’re getting their money back.

If you got the refund in the form of a paper check (how old school), write “void” in the check’s endorsement section, then return it to the IRS. Send it back to the city where the IRS sent it from, which you can see on the bottom of the check in front of the words “tax refund.” The IRS has a list of mailing addresses at the bottom of this release.

According to The New York Times, you’ll also want to get in touch with the IRS to find out whether or not the scammers actually filed a fake tax return under your name and Social Security number, since some scammers might file a fraudulent return under one name and send it to a bank account that’s under another. If they did file a return under your name, it'll complicate the process of you filing your real returns this year.

Whatever you do, don’t spend the money—you’ll have to return the money to the IRS and, adding insult to injury, you may have to pay interest on it to boot.

And if you haven't gotten a bogus refund? This may be the kick in the pants you need to get you filing your taxes as early as you can.

[h/t WIRED]