Computer users in the UK are being urged by the National Crime Agency to act now to protect their desktop machines and laptops from a new computer virus.

More than 15,000 computers are already believed to have been infected with the virus, which is attacking the Windows operating system. This includes users who run Windows on Apple Macs and those who have embedded the system into a company server.

The virus, typically downloaded through a bogus email attachment, contains the following two types of malware:

  • The Gameover Zeus virus, which enables criminals to take control of your computer. Once they've done this, they can then access files stored on your computer, look at your bank or credit card accounts and send emails in your name.
  • A program known as CryptoLocker, a piece of 'ransomware' that then enables criminals to effectively lock down your computer. They'll then issue a ransom demand – probably for hundreds of pounds. It'll say that if a sum of money is paid out, you'll get control of your computer back – although there are no guarantees this will happen.

In the current attack, Gameover Zeus (also called GoZeus or P2PZeus) searches your machine for data. If it doesn't find enough information worth stealing, CryptoLocker will kick in and the computer will be held to ransom.

The NCA says it and America's FBI have taken temporary control over the communications which the criminals are using to connect with infected computers.

But it says they're only able to do this for two weeks, so computer users are being urged to protect their devices now and to remove the virus if they've been infected.

The NCA says: "This warning is not intended to cause you panic but we cannot over-stress the importance of taking these steps immediately.

"This is because the NCA has taken temporary control of the communications used to connect with infected computers, but expects only a very limited window of opportunity to ensure you are protected."

How do I protect myself from the virus?

The NCA, in conjunction with the Government's Get Safe Online help website, is urging computer users to do the following:

  • Make sure internet security software is installed and updated by running scans and checking your computer operating systems and software programs are up-to-date. See our Free Antivirus Software guide for a full list of free and legal programs.
  • Back up all important information such as files, photos and video, in case your PC is locked by CryptoLocker.
  • Only open email attachments if you're 100% certain the email is authentic, as doing so could download the virus. It could also be a phishing scam trying to trick you into giving out personal details. See our Phishing Scams guide for more on these.

How do I check if I've got the virus?

Some internet service providers (ISPs) have already contacted users to tell them they're affected. Even if you don't get one of these emails, the NCA is still urging all users to run one of the specially-created tools below.

You can use any of these tools to check if you're affected, regardless of which security program you currently use:

  • F-Secure Online scanner (Windows Vista, 7 and 8) and F-Secure Rescue CD (Windows XP systems).
  • Heimdal Security (Microsoft Windows XP, Vista, 7, 8 and 8.1).
  • Use Kaspersky if you think your computer is infected with Gameover Zeus and WindowsUnlocker if your computer is infected with CryptoLocker.
  • McAfee.
  • Microsoft Safety Scanner (downloaded onto Windows 8.1, Windows 8, Windows 7, Windows Vista, and Windows XP).
  • Sophos (Windows XP (SP2) and above).
  • Symantec.
  • Trend Micro (Windows XP, Vista, Windows, Windows 8/8.1, Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2).

What if I'm a victim?

If you've checked your computer and found you're a victim, you can use any of the tools above to remove both Gameover Zeus and CryptoLocker.

If you think you've lost money through this virus attack, or any other, you should report it as soon as possible to Action Fraud via its website or by phone on 0300 123 2040.

Internet safety tips

Even if you've not found this virus on your computer, it's good practice to keep your internet security system up-to-date. See our Free Antivirus Software guide for a full list of free and legal programs.

Files such as documents, photos and music should always be backed up and it's important to never store passwords on your computer in case it's accessed by criminals.

Your passwords should also be chosen carefully so they aren't easy for hackers to guess. Here are some tips:

  • Make sure it isn't obviously associated with you. Avoid using your date of birth, pet's name, or any other information hackers could easily access on a social network or by going through your bins.
  • Use a mixture of words, numbers and characters. Passwords can still be memorable even when you jumble up numbers and letters, for example: M0n3y5av7ng3xp3rt.c0m!
  • Use different passwords for different sites. This ensures that if someone were to guess one of your passwords, they wouldn't be able to get into all your accounts.
  • Keep them safe. If you're using lots of different passwords, it's tempting to write them down. But that can be dangerous. So try to use a piece of technology that requires a password to get to the passwords.