It’s a bad idea to ever use the word “yes” when talking to any telemarketer, but with the latest version of an old scam, saying “yes” can quite literally come back to haunt you.

Here’s how the scam works: you may receive a phone call from an automated system (a robocall) or a live person, but the common thread will be that the caller will ask, “Can you hear me?”

“Yes,” you respond, because you heard the question. Now, according to police departments across the country, that means that the scammers now have a recording of your voice saying “yes.”

Even if you never agree to buy anything, you might later find out you’ve been signed up for a home alarm system, a cruise, some added service for your phone, or any other thing you couldn’t possibly want.

If you dispute the charges, the company could take legal action, sticking that recording of you saying “yes” into a recording of a different conversation as evidence that you agreed to the transaction.

Another variation uses that recording to “prove” that you agreed to charges on a credit card of yours when the perpetrators have already stolen the number. This is similar to a scam we wrote about in 2010, where scammers posed as pollsters, asking people if, for example, they had a dog.

READ MORE FROM CONSUMERS UNION: How the phone companies can help end robocalls

What should you do? Hang up. Screen your calls, avoiding numbers that you don’t recognize. Use a robocall-screening service if there’s one available to you. Scammers will use a fake number from an area code close to you, to make you more likely to think it’s a local business and pick up. Be cautious and don’t answer questions from strangers.

If you have any doubt and think that the call could be legitimate, you can try answering the question without saying the word “yes.” For example, you could say, “I can hear you.”

In general, though, we think it’s best to keep to one simple rule: never say yes to telemarketers, whether they’re robotic or not.

Update: We’ve heard from some readers who are skeptical of this warning, doubting the mechanics of the scam. It’s better to be aware of a possible scam than to not be aware of it, and if the publicity around this warning reminds one person not to talk to or engage with robocallers or telemarketers, then it’s a net positive.

The technique of playing a fraudulent recording has been employed in the past: In the case FTC v. Sun Bright Ventures, “telemarketers falsely told consumers they needed their bank account numbers to verify their identities before sending a new Medicare card, promising they would not take money from the accounts. In fact, they took several hundred dollars from each consumer’s account and provided nothing in return. In some cases, their telemarketers falsely promised to provide consumers with identity theft protection services.”

According to the FTC’s Telemarketing Sales Rule, “an 82-year old victim filed an affidavit with his bank, contesting two remotely created checks made out to the defendants for $448.52 each. Initially, the bank reversed the charges and returned the money to his account. However, a few months later, the bank revoked the credit to his account because it received a voice recording of the consumer answering the defendants’ “yes” or “no” questions purportedly authorizing the debits. The bank revoked the refund despite the consumer’s allegations that the tape was fraudulent, noting several discrepancies including the fact that he never verified his age as between 18-75, when he was in fact 82 years old, and that the representative’s voice on the recording was a woman’s, instead of the man with whom he had spoken.”

In other words, just hang up.