Viruses, Malware and Trojans

Viruses and attacks from hackers are a potential threat to all computer users. Learn about how they work and how to protect your computer and your personal information from unwelcome visitors.

What is 'malware'?

Malware or ‘Malicious Software’ is software designed to secretly access a computer system without the user's consent. Types of malware include computer viruses, worms, trojan, spyware and other malicious or unwanted software.

A computer virus is a software program that can copy itself and infect a computer. Viruses can spread from one computer to another when a user sends it over a network or the Internet, or carries it on a CD, DVD or USB drive.

A computer worm is a malicious program that differs from a virus in that it can spread automatically over networks without the intention of users. They are designed to replicate and transmit by themselves, allowing them to spread very quickly. Worms cause long delays in downloading and viewing web pages, as they often arrive in large volumes, blocking the networks.

A Trojan is a form of malware which automatically installs a program onto the computer. Hackers then use the program to gain control of a user’s computer.

Trojans are often quietly bundled with software or files a user genuinely wishes to download or install. Trojans are often installed from:

  • Peer-to-peer movies or software downloaded from the internet
  • Pirated software
  • Email files
  • Files sent via online messaging or voice-over-internet services

Trojans enable a hacker to remotely access a user’s computer system and:

  • Steal data from files on the computer (e.g. passwords or credit card information)
  • Download or upload other malicious files onto the user's computer
  • Modify or delete files
  • Log keystrokes (i.e. recording all keystrokes made on the computer, then mining that data for online passwords, such as internet banking)
  • Enable hackers to watch a user's screen - this can give hackers access to passwords and user names through click-based password entries
  • Crash the computer
  • Use the machine as part of an automated spamming campaign, or register sites with illegal content (so that the hacker cannot be traced)

Spyware is software that displays advertisements or tracks personal or sensitive information, accessing a computer system when installing a new program (often downloaded from the internet). Spyware secretly gathers information about the user and can make changes to the configuration of a computer, causing it to slow down or crash. These programs can also change a Web browser's home page or search page.

How do you know if malware is active on your system?
How does malware spread?
What should you do if you suspect malware on your computer
How can you protect yourself against malware?

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