Carlos Tapang, the founder of Pure Money Technology, claims the Bellevue telecom carrier didn't protect his phone number, allowing hackers to gain access to his online accounts.

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The founder of a Bellevue technology company is suing T-Mobile, claiming the telecom provider allowed hackers to gain control of his cellphone number and steal more than $20,000 worth of cryptocurrency.

Carlos Tapang filed the suit against the Bellevue-based wireless carrier this week after he lost control of his phone number in early November, which led to losing access to most of his online accounts.

On Nov. 7, Tapang and his family members noticed their phones had restarted and been wiped of information. They were no longer on the T-Mobile network.

Tapang contacted the carrier and found  that his phone number had been transferred to AT&T. T-Mobile was able to get the phone numbers back the next day, but in the meantime, Tapang was locked out of his Microsoft and Google email and storage accounts and some of his cryptocurrency accounts had been drained.

Once the thieves had access to his phone number, they were able to request a password change and reset the security on many of his accounts, locking him out,  he said.

The thieves sold virtual money in his online wallets for 2.875 bitcoins, Tapang claimed in the lawsuit. That amounted to about $20,466 on Nov. 7, according to historical bitcoin data from Coindesk.

It is unclear exactly how the thieves gained access to Tapang’s accounts, but the lawsuit suggests they impersonated him to T-Mobile customer-service agents and requested that the phone number be transferred to their own device on the AT&T network.

Tapang claims he had told T-Mobile to require a pin number from him, as an extra form of security,  before making any account changes. The company failed to ask for the pin number, the lawsuit claims.

“Despite having asked T-Mobile for additional security, Mr. Tapang lost his phone number and many thousand dollars’ worth of virtual currency,” it reads.

T-Mobile has not filed a response in court. The company declined to comment Wednesday because the litigation is pending, a spokeswoman said.

Tapang is the founder of Pure Money Technology, a company that encourages merchants to accept cryptocurrencies.

In a Nov. 30 post on LinkedIn, he outlined his ordeal trying to regain access to his online Microsoft and Google accounts after his cellphone number was hijacked. One of the biggest things he learned, he wrote, is that two-factor authentication is not secure enough.

The case is filed in U.S. District Court in Seattle.