There’s a new phone scam tactic out there and it’s increasing at a rate that has security experts, law enforcement, and even the banking and financial sectors alarmed. It’s called spoofing, and the consequences range from annoying to life-threatening.

Spoofing occurs when a person manipulates their phone in order to use someone else’s existing phone number to initiate a call to their intended victim. Scammers often use automated software to conduct these spoofed calls, meaning they’re not even sitting at a telephone and dialing the numbers. They can pull off millions of fake calls every month, as one security company found. When you receive a call like this, your caller ID may indicate an individual’s phone number, a company or business phone number, or even a message indicating it’s an unknown phone number, but it’s really someone else on the other end of the line.

The real danger is from a scammer whose phone number makes him appear to be from your bank or credit card company, making you more likely to believe whatever lie he’s about to tell you and trick you into handing over your personal information. Another issue with spoofing is that the caller will wait until you answer and then simply hang up. When you call back, thinking the call was accidentally disconnected, you’re actually calling a foreign country and paying international calling rates.

Unfortunately, another use scammers have for spoofing is simply to pull of spiteful pranks. One man in Washington used spoofing to inform the police he was holding hostages at a certain address. By the time the scenario had ended, a SWAT team had broken into the home of an unsuspecting family, which could have had deadly consequences. A Colorado Springs woman had her phone number stolen and used to call countless people over and over; the multiple victims then called her back repeatedly to tell her to stop harassing them, and some of those callers even threatened her life if she didn’t stop calling them.

So how do you protect yourself from spoofing? If you’re the one receiving the calls, the end result of having your phone number randomly stolen for illegal purposes can be upsetting, and more than one individual has had to change her phone number in order to make it stop. Be sure to report it to law enforcement and your phone provider, though; some scammers have employed phone spoofing in order to commit crimes like fraud, and you want to make sure there’s a record that you were the victim, not the perpetrator.

If you receive a phone call from an unknown number, feel free to ignore it. If it was actually a legitimate and important communication, they’ll leave a message, but be sure you call the number that you have on file if it’s from a business, and not the number that appeared on your caller ID. If you receive a call from a number you know, however, like your bank or credit card company, remember to NEVER give out sensitive information like your account number, your PIN number, your Social Security number, or other personal data. If they’re really calling from your bank, they already have that information and there’s no reason for you to provide it. For many companies, asking for this data actually violates protocol, so the only person who would ask for it is a thief.