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Malware (short for 'malicious software') is software that cybercriminals use to harm your computer system or network. Cybercriminals can use malware to gain access to your computer without you knowing, in targeted or broad-based attacks.

Malware is the term used to refer to any type of code or program that is used for a malicious purpose.

Cybercriminals use malware for many different reasons but common types of malware are used for stealing your confidential information, holding your computer to ransom or installing other programs without your knowledge.

Use this guidance to learn about malware and how to protect yourself.

Tip: You can protect yourself from malware by using anti-virus software and safe behaviour online.

Protect yourself from malware

Take the following steps to significantly reduce your risk of being affected by malware:

Prevent malware by installing applications safely

Malware is distributed in several ways:

  • By spam email or messages (either as a link or an attachment)
  • By malicious websites that attempt to install the malware when you visit, by exploiting weaknesses in your software
  • By masquerading as a good application you download and install yourself. Some malware even pretends to be anti-virus or security products.

Protect yourself by only installing the files you need and sourcing them from well known and legitimate app stores.

  • Don’t download applications from third-party download sites.
  • Don’t click on online ads to download applications and do use ad-blocking software.
  • Don’t download and install applications from peer to peer networks – you never know who has changed the files.
  • Don’t click on links in emails or instant messages, or execute attachments unless you are sure they are legitimate. Use a spam filter to protect yourself from malicious messages.
  • Don’t install applications received from contacts, say via email or USB sticks, without scanning them with your anti-virus application first.

Learn more about malware

There are many different types of malware but most are used to either steal your information, your computer’s resources or your money. This table lists some of the most common types of malware affecting people and businesses in the wild today.

Type What it does
Trojans and backdoors

Traditionally trojans were programs that appear to serve a useful purpose but do something malicious when run. Trojans may steal information, download additional malicious files or even provide a ‘backdoor’ into your computer for a hacker – allowing them to do almost anything they like.


Malware that makes your computer or files unusable until you pay a fee. Essentially extortion by malware.


Logs every keystroke you make and then sends that information, including passwords, bank account numbers, and credit card numbers, to scammers for fraudulent use.

Viruses and Worms Viruses are malicious programs that infect files, inserting themselves into the file’s code and then running whenever the file is used. Worms are standalone malicious programs that spread themselves from computer to computer. Similar to trojans, viruses and worms can have many different payloads – for example, they can steal your information, download and install other malicious files, delete your files or even send spam.

The following signs may indicate there is malware on your computer:

  • your web browser starts on a different homepage than normal
  • your files are inaccessible
  • random error messages appear, or
  • new programs, toolbars and icons have been installed.

To check if your computer is infected run a full scan using your anti-virus software and follow the instructions to remove it. 

Read the UK NCSC guide on mitigating malware

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