A virus that turns victims' computers into a cryptocurrency miner without their knowledge is spreading across Facebook Messenger, security experts have warned.

The malware, named "Digmine", affects desktop versions of the app when running on a Google Chrome browser, according to researchers at Trend Micro.

"If the user’s Facebook account is set to log in automatically, Digmine will manipulate Facebook Messenger in order to send a link to the file to the account’s friends," they wrote in a blogpost.

Crypto-mining malware works by hijacking a computer's processing power to help generate coins and confirm transactions for digital exchanges.

Effectively, it is keeping the lights on for the blockchain, the digital ledger that keeps record of cryptocurrency like Bitcoin.