Malware is malicious software that is created by fraudsters and criminals to infiltrate computers. It can take many forms and is used for a large number of illegal purposes such as stealing personal information, deleting or corrupting data, creating botnets (networks of infected computers) and bypassing security software.

There are many forms of malware and this section will give you information on the most common types and what you can do to avoid them.

Fraudsters send millions of spam emails to UK customers, claiming to be from financial institutions. The emails have attachments which claim to have details about, for example, a suspicious transaction, an invoice, fax, voicemail as well as other details.

Opening the attachment could lead to malware such as ‘Cryptolocker’ being installed on your computer. This malware will encrypt the files on your computer, and network drives the computer is attached to, before demanding payment to release the files. Once the files are encrypted, there is no way to decrypt them without paying the ransom.

For more details about spam campaigns, please visit Action Fraud.

Anyone who is infected with this type of malware should report it via -


Computer viruses are something most internet users are aware of and, thanks to anti-virus software and firewalls, protection is available.

However, the people who create these viruses are constantly looking for new ways to spread them onto our computers. 

What is a virus

A virus is a software programme that can reproduce itself and often carries harmful malware that could do harm to files and programmes on your computer. Viruses can be used to track what you do on your computer and allow unauthorised and potentially malicious access to your personal computer.

How to recognise a virus/trojan

If you have a virus on your computer you may notice:

  • Your computer behaving strangely
  • Music starts playing on its own
  • Messages and pop ups are displayed
  • Files may be changed or deleted
  • Your hard drive has been damaged or wiped
  • Your computer is slow and unresponsive

How to avoid viruses/trojans

  • Make sure you have supported anti-virus/anti-malware software installed on your computer.
  • Make sure the anti-virus/anti-malware software is up to date with the latest definitions from its vendor.
  • Make sure you run a full scan, on a weekly basis.
  • Make sure that any files or programs you download from the internet are from legitimate sources.
  • Avoid downloading pirated files (including movies, music and computer software). While they may be free, they may also contain hidden malicious software.
  • You should always ensure that common software applications and plug-ins such as Microsoft Office, Adobe Acrobat and Adobe Flash are up to date and have all security patches applied. Many applications give the option for updates to be automatically applied.
  • Make sure you install all the latest security updates for your internet browser (e.g. Internet Explorer) and operating system (e.g. Windows XP) in a timely manner.You can usually upgrade your browser version from your browser providers' website. Here are the most common providers*:
    Upgrade your Internet Explorer browser
    Upgrade your Mozilla Firefox browser
    Upgrade your Safari browser
    Upgrade your Chrome browser
    Upgrade your Opera browser


When spending time online you can often be bombarded with requests for you to download files such as desktop wallpapers, screensavers and widgets. However, if you decide to download anything such as pictures or files you could be downloading a trojan.

What is a trojan

A trojan, as the name suggests, is a malicious computer programme pretending to be something it's not and which includes a hidden program designed to do harm. A trojan can cause different levels of harm to your computer for example:

  • Erase or overwrite data on your computer
  • Record keystrokes to get your personal information
  • De-activate your firewall and your anti-virus software
  • Install other viruses

Since trojans come in so many different forms there is no one foolproof way of getting rid of them and they can be very hard to remove. Using anti-virus software and ensuring it's kept up to date is the best defence against Trojans.

How to recognise and avoid a trojan

Trojans can behave in very similar ways to viruses. Please read through the Virus section to find out how to recognise and avoid a trojan or virus.

Spyware/ Adware

The internet is great as a forum for people to share information and helpful programmes they’ve developed. Unfortunately something that looks helpful or fun like browser toolbars, weather programs and screensavers might instead be a carrier of spyware or adware.

Spyware is software designed to spy on your online activity and adware is software designed to install pop ups and advertising on your computer. Many of these viruses do both.

What is spyware/adware

At best, the spyware can be fairly harmless - it might collect information about your browsing habits and display advertising targeted to your interests (adware). Even so, it does feel like an invasion of privacy and it may well slow down your computer.

At worst however, spyware can be malicious, it may scan your hard disk to try and capture your personal information, such as banking details and passwords, and transmit them to criminals. It may also try to shut down your anti-virus or anti-spyware programs.

Ways to tell if you have spyware/adware

  • You see pop-up adverts (adware) even when you're not browsing
  • Your browser's start page or search settings change without warning
  • A new toolbar appears in your browser that you didn't expect or want 
  • Your computer starts to run more slowly or crash more often

How to avoid spyware/adware

If you follow this advice it will also help keep you safe against other online problems.

  1. Download and install anti-spyware protection
    Microsoft offers a free anti-spyware program, Windows Security Essentials, to Windows users.  Other software providers offer similar products - any reputable computer software supplier can recommend the most suitable one for your system.
  2. Keep your software up to date
    Make sure the software on your computer, particularly the operating system, is up to date.  If you're running Windows, you can download updates from the Microsoft security site*. You can use this site to allow your computer to receive updates from Microsoft automatically, so you won't have to remember to download them.
  3. Surf and download safely
    Only download programs from websites you trust.  If you're not sure whether a particular program is safe, you can enter the name of the program into your favourite search engine, to check if anyone has reported that it contains spyware

Read all security warnings, license agreements and privacy statements associated with any software you download

Never click 'OK'  or 'I agree' in a pop-up window on the internet unless you are sure what you are agreeing to

Be wary of 'free' music and movie file-sharing programs and make sure you understand the software that comes packaged with these programs.


Scareware, also known as rogueware or fake anti-virus software, is one of the fastest-growing types of internet fraud.

It has been estimated that 35 million PCs worldwide (3.5 per cent of all computers), are infected with scareware, netting more than $400 million a year for cyber criminals.

What is it?

Scareware is a type of malware that generates pop-ups resembling Windows system messages, pretending to be anti-virus or anti-spyware software, a firewall application or a registry cleaner. The messages usually trick users into believing that their computer has a large number of infected files. The user is then advised to purchase software to fix the problems. However, in reality the problems do not exist and the recommended software download is likely to contain real malware. If the user falls for the scam, they will lose any money they paid for the useless software and may have their payment details sold to other fraudsters. Once infected, the machines can become virtually impossible to operate.

How to avoid scareware

Always ensure that you have legitimate anti-virus and anti-malware software installed on your computer. Contact your internet service provider to see if they offer free security software or have special deals internet security software.

Never click on a pop-up that claims your computer is infected or offers to scan your machine for errors. They are almost always scams.

*Links to external sites are provided as part of our commitment to making online banking safe and secure. However, we cannot accept responsibility or liability for the content or availability of external sites. We cannot guarantee that any software downloaded from these sites will work, or be free from viruses or malicious code.


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