SOPHISTICATED cyber criminals are accessing people’s computer systems and holding their files to ransom, a new warning from police has revealed.

The scam was first spotted a few months ago when victims were being forced to pay hundreds of pounds to have their files released by the extortionists.

Detective Chief Inspector Paul Williamson, head of Warwickshire and West Mercia Police's cyber crime unit, said a programme called CryptoLocker was being used to target personal computers using Microsoft Windows to make damaging changes which usually only they can reverse.

DCI Williamson said: “It’s ill-advised to pay this ransom because there is no guarantee they’ll send you the key and if they do, they know you are susceptible to blackmail and they may strike again.

“Making payment will only encourage them to carry on. If no-one pays they will stop the practice.”

The malicious software was not a virus and got into computers through an email attachment.

Most of the reported victims lacked up-to-date security and anti-virus protection on their computers.

After blocking all data on a computer, a message flashed up on screen saying the personal files had been encrypted with a deadline to pay around £200 to have them released.

People are urged to use precautions, including backing up files on an external hard drive, uploading files and photos to online accounts, changing to a safer email service, not accessing pornographic or not trusted websites, update the operating system and internet browsers, set up System Restore points, act quickly in running a virus programme is a questionable file is downloaded, and encrypt files and the computer system.