NEW YORK (CBSNewYork) — Prosecutors say a man targeted hundreds of people across the country in a sophisticated scam, using cell phone numbers to access bank accounts.

Kim Pilson, of the Upper East Side, knows what it’s like to be hacked.

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“I have been scammed where someone found my ATM card number somehow and was able to make a duplicate card and start using my cash,” she said.

Wednesday, the Manhattan District Attorney’s office announced an even more sophisticated scam called SIM swapping.

Joseph Chase Oaks, from Alabama, is charged with grand larceny and identity theft, accused of targeting 300 people in New York and across the country to steal identities and $150,000 in cryptocurrency like bitcoin.

“I think it’s a terrible thing. In the pandemic, people don’t have money as it is,” one woman said.

“What is SIM swapping?” CBS2’s Jessica Moore asked tech expert Roger Cheng.

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“SIM swapping is the act where a hacker will call up a carrier and actually convince them that they are, in fact, you,” Cheng said.

He says all a hacker needs is a victim’s phone number and enough personal information, which is often found on the internet, to pass themselves off as their target and convince the phone company to transfer the contents of the victim’s phone onto the hacker’s phone.

“Once you have the phone number, once you have a person’s account, it’s essentially the keys to the castle. You can access a lot of things with that cell phone number,” Cheng said.

Cheng says people should create a PIN or passcode to add an extra layer of protection to their phone accounts.

“So it’s not just, you know, your address or your email, some sort of personal PIN or passcode that isn’t found on the internet. It’s an extra step and it is another thing to remember, which I get is a hassle for a lot of people, but when it comes to protecting yourself from SIM hacks, that is a really key protective measure,” he said.

“They need to make people aware that this is a possibility so if their cell service goes out, people know what to do right away because they might not know that it’s because they’ve been scammed,” Pilson said.

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Oaks pleaded not guilty and was released on his own recognizance. He will be back in court in April.