Flickr/John Mason People who work in the City of London, the UK capital's financial centre, are being targeted by a specific kind of computer attack that holds digital files to ransom.

Cybersecurity company Malwarebytes says that the City of London is a hotbed for ransomware attacks compared to the rest of Europe.

The company monitored cybersecurity threats for just over a year to see which parts of Europe had the most attacks. It found that the City of London suffered 10,500 ransomware attacks, which is 670% more than the second-biggest target, Manchester.

Ransomware is where a hacker attempts to install a specific kind of malware that encrypts a user's files and then holds them to ransom. The target usually has to pay a ransom in Bitcoin to get their files back.

File Cryptor is the most common type of ransomware used, followed by File Locker, Trojan Ransom, TeslaCrypt, and Cryptowall.

Malwarebytes CEO Marcin Kleczynski told Business Insider in August that he's aware of banks that have been stocking up on bitcoins in case they're hit with ransomware attacks. "I talked to a couple of banks and they say they have 50-100 bitcoin ready at all times in a wallet to deploy if a ransomware attack hits," he said.