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A Guide to Viruses

What are viruses?

Viruses are programs that replicate themselves and make changes to computer systems. Quite often viruses cause damage to the infected system by deleting important system files or corrupting data. Some viruses seem harmless and just display a message on screen. However, even these may unwittingly cause data loss through system crashes.

Originally viruses would spread by infecting executable programs such as those ending in .COM and .EXE on PCs. They could also infect areas of the hard disk or floppy disk used for booting the operating system. With the introduction of macros to popular software such as the Microsoft Office suite of applications, new viruses appeared taking advantage of this new method of executing themselves. This is now one of the most common types of true virus, costing businesses millions each year.

The word virus is also used as a generic term to describe other malicious software, such as Trojan horses, worms and hoaxes. Trojan horses refers to software which disguises itself as something different, to make an unwitting user run the malicious program. Examples of Trojan horses include files within compressed archives (such as ZIP files) which can be mistaken for harmless files such as “readme.txt                      .exe”. A “txt” file is just a text file which cannot be executed. But this file actually ends in “.exe” which makes it an executable file.

A worm replicates itself, typically through email or by attacking other computers over a network and then running itself on the newly infected computer. Worms have been in the press a lot in the last few years, with large-scale infections due to likes of “Melissa” and “Nimda”.

Hoaxes can sometimes be difficult to spot. Typical hoaxes will appear to have come in the form of an email from a colleague, telling you about a new virus and how to prevent it from spreading by deleting a certain file. The file will usually be something required by your operating system that will cause serious problems when it is deleted.

Adware installs itself on your system and often hooks itself into your web browser. As a result, whenever you browse the web, extra pop-up windows appear with adverts. When installed, spyware collects information about you, such as details of websites you may visit, and sends this information off to a server on the Internet. Adware and spyware are not always detected by anti-virus software.


How do I protect myself?

By following a few simple rules, you can minimise the risk of infection.

  1. Install anti-virus software. Some software is free for home users, such as Grisoft’s AVG. When installed, make sure it is regularly updated to ensure protection against the latest viruses.
  2. Run regular scans on your files. If you do not have anti-virus software but do have an Internet connection, free online scans are provided by Symantec and Trend Micro. Even if you do have anti-virus software, it is worth running scans using another vendor as a double-check.
  3. Install a firewall. This will prevent remote attacks exploiting weaknesses in your operating system.
  4. When receiving files, either by email, web browser, or floppy disk, scan them for viruses. Trend Micro’s online virus scanner can be used to scan a particular directory or drive.
  5. Try and avoid receiving files in formats that may allow code to be executed, such as Microsoft Word documents. Adobe PDF files could be used instead if the file does not need to be edited again.
  6. Adjust your security settings so that code is not automatically executed in programs such as Microsoft Outlook as well as other Office applications.
  7. When browsing websites, beware of software that may try to automatically download itself. This is typically used by adware and spyware.

Where can I find out more?

The following website links can be used to find out more information about viruses and anti-virus protection :

Symantec Security Response

http://securityresponse.symantec.com/

Information about the latest virus threats, free online virus scan, encyclopaedia of viruses and some removal tools.

Trend Micro Housecall

http://uk.trendmicro-europe.com/enterprise/products/housecall_launch.php

Alternative free online virus scan which allows you to specify where to scan. This online scanner also detects some adware. Elsewhere within the site you can also find virus threat alerts and a virus encyclopaedia.