San Francisco (CNN Business) Robert Ross was sitting in his San Francisco home office in October 2018 when he noticed the bars on his phone had disappeared and he had no cell coverage. A few hours later, he had lost $1 million.

Ross was the victim of a SIM hack, an attack that occurs when hackers take over a victim's phone number by transferring it to a SIM card they control. By taking over his cellphone number, a hacker was able to gain access to his email address and ultimately his life-savings, Ross said in an interview with CNN Business.

"I was at home at my desk and I noticed a notification on my iPhone for a withdrawal request from one of my financial institutions, and I thought, 'That's weird. I didn't make a withdrawal request,'" Ross recalled. "Then I looked back at my phone and I saw that I had no service."

In recent years, cybersecurity breaches have become so common that some consumers may almost take for granted their information has been compromised at some point. The list of massive data breache s includes a major hotel chain, a credit reporting firm, a bank and a social network. But SIM hacks are both less talked about and yet potentially more devastating.

There is limited data on the prevalence of SIM hijacking nationally, but during the last year, the US Department of Justice has indicted numerous people for crimes associated with SIM swapping.

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