The National Crime Agency is warning people they have two weeks to save their computers from a powerful malicious software attack. The malware called GOZeuS is hiding within attachments in emails and, once downloaded, enables hackers to access computers and scan them for valuable information.
If no data is found, a second malware, known as CryptoLocker, locks the computer, displays a window with a countdown, and demands a ransom to grant access again.
According to the NCA, people are asked to pay 1 Bitcoin (£200 - £300) to regain access to their files.
The NCA is advising people to make sure security software is installed and updated, by running scans and checking that computer operating systems and applications are up to date.
Computer users are constantly being told to change passwords and update software due to the latest "Trojan" or "Bot" - but what are they?
The malware, called GOZeuS is hiding within email attachments, and once downloaded will enable hackers to mine infected computers.