• Federal investigators filed a warrant for 10.2 bitcoin held in a Huobi Global wallet.

• The cryptocurrency was stolen from a Coinbase account in an $11.6 million heist, officials said.

• Investigators said an unknown person sent a notification to a Coinbase user after a 200 bitcoin buy.

A federal judge this month approved a warrant to claw back more than $600,000 in bitcoin from a Huobi Global wallet, after federal investigators said it was part of an $11.6 million haul stolen from a Coinbase account.

In April, after a Coinbase user bought 200 bitcoin, a notification popped up, alerting them that their account had been locked, said a complaint filed by the US attorney's office in Los Angeles. Although the notification appeared to be from Coinbase, it wasn't.

Instead, the notification was the first step in an alleged fraud. In the moments that followed, almost $11.6 million in crypto, about 206 bitcoin, was removed from the user's account, investigators said.

It's unclear how the alleged fraudster knew about the Coinbase transaction and whether the online notification mentioned in the warrant appeared on a phone or computer. Coinbase declined to comment.

The Coinbase user, who was identified in court documents only as G.R., called a phone number on the notification, thinking it would connect to a Coinbase customer-service representative, said a federal complaint filed by investigators last month.

An "unidentified individual 1," or "UI-1," answered the call and asked G.R. to make a series of changes to the account, the complaint said.

Those changes included allowing remote access to the account, the complaint added.

"Once granted access to the Victim Account, UI-1 increased the daily transaction limit and also attempted to deactivate certain notifications and alert settings on the Victim Account," Dan G. Boyle, an assistant US attorney, wrote in a document filed in US District Court for the Central District of California in September.

Within moments, millions in bitcoin and XLM were removed from G.R.'s Coinbase account, investigators said.

"The total value of virtual currency transferred out of the Victim Account between 2:02:40 PST and 2:12:41 PST on or about April 20, 2021, without G.R.'s authorization was approximately $11,570,138," they wrote in their complaint.

The money was then moved by an unknown person through a series of transactions between several accounts. About 10.2 bitcoin ended up in an account with Huobi Global, one of the world's largest exchanges, investigators said.

The investigators filed a forfeiture notification, seeking to reclaim those bitcoin. Huobi Global didn't respond to a request for additional information.

In early October, Judge Dolly M. Gee approved the warrant request, and a notice was posted in case anyone other than G.R. wanted to claim ownership of the 10.2 bitcoin.

"Huobi has agreed to maintain a freeze on the funds pending resolution of the forfeiture action," Thom Mrozek, the director of media relations for the US attorney' office in Los Angeles, told Insider via email. "No one has been arrested or charged, but our investigation is ongoing."

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