Spanish telecoms giant Telefonica is facing an 85 percent computer shut down after hackers infiltrated its systems demanding $550,000 in Bitcoin.

As local news resource El Mundo and others report, the attack, which occurred earlier Friday, has resulted in most staff abandoning their positions and nine out of 10 company machines infected.

Hackers are demanding a payment of $300 per machine, roughly equal to 300 Bitcoins currently worth around 510,000 euros.

Telefonica is a multinational corporation, subsidiaries of which include major European mobile operator O2, Movistar and Vivo.

“The origin of the infection is not confirmed at the moment, but sources close to the company point out that it is being treated as an attack originating in China,” El Mundo writes.

Telefonica’s chief data officer Chema Alonso meanwhile took to Twitter to state that the attack had been “overblown” by the media.

“Our colleagues are working on it right now,” he said, adding that the problem had “unfortunately affected other organizations” and that the company was working with the victims.

…en la casa. Las noticias son exageradas, y los compañeros están trabajando en ello ahora mismo. Por desgracia, también ha afectado a otras — Chema Alonso (@chemaalonso) May 12, 2017

The success of the attack is thought to be due to a vulnerability in Microsoft Windows. The events mark a further instance of Bitcoin ransomware being used for considerable gain, studies previously showing that companies often choose to pay the price in order to regain control quicker.