Stolen bitcoins have been spotted moving on the blockchain after three years of lying dormant.

In a series of transactions beginning at 06:00 UTC Friday, 172.54 BTC or about $1.37 million moved from a wallet that had previously held funds taken in the 2016 Bitfinex hack. The theft, which cost the exchange $60 million, remains unsolved.

The Twitter handle Whale_Alert noted the transfers this morning. They continued throughout the day, ending with a $137,514 transaction at 19:47 UTC.

Hard Fork posited that the move was connected with Bitfinex’s Leo token, which allows for the anonymous return of stolen funds. Bitfinex spokesperson Anneka Dew denied that the exchange was involved in the move.

“We are not involved, and the movement is not tied to the procedure outlined in the UNUS SED LEO white paper,” she said.

Given the anonymous nature of bitcoin wallets, these moves are the only evidence of hacker activity after the theft. They can be used for forensic analysis by blockchain sleuths but often instead result in money laundering activity to hide the funds’ ultimate destination.

The Bitfinex theft was the largest loss of bitcoins by an exchange since the Mt. Gox hack in early 2014 (worth $350 million). In February of this year, U.S. law enforcement retrieved 27.66270285 BTC that had been taken from Bitfinex.

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