Anti-virus and firewall software can protect your computer from online threats. Occasionally a threat can sneak through the defences but the good news is that most threats can be easily eliminated once spotted. Here is a guide to the types of infection it's worth immunising against.

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The Knowhow

Below is a list of online threats and how they work:


A virus is a program that copies itself onto your system and spreads onto other computers through networks, discs, emails, the internet and any other way it can. A virus usually has a specific purpose; from just drawing attention to its self via pop-up windows, right through to posing a risk by creating permanent damage to your personal files and folders - a virus can even completely stop your computer from working.

  • Macro drive: One of the most common viruses, the Macro drive is designed to exploit Macro functions in Microsoft Word, Excel and Access, leaving other programs vulnerable. This virus infects your data files and can prove very expensive for businesses, in terms of lost files and the time taken to clean up the damage.
  • File infector: This virus infects program files with .exe and .com extensions, preventing you from running programs installed on the computer. The virus is memory resistant and once opened will quickly spread and infect all program files on the hard drive.
  • Boot sector: Boot sector viruses hide in the computer's memory and can overwrite boot files, preventing your computer from loading correctly. Viruses of this type usually infect your computer by floppy drive and hard disks.
  • Master boot record: These infect the computer the same way as a boot sector virus, telling the computer how to load the operating system. The virus overwrites this command and instead instructs your PC to save a copy of the original file in a completely different location.
  • Multi-partile: These types of viruses infect both program files and boot records and are notoriously difficult to get rid of. If you manage to clean one and not the other, the computer will become re-infected.

Thankfully, viruses can be prevented and removed with up-to-date anti-virus software. For more information on virus checkers, read our article; Anti-virus software: What you need to know


Malware is a generic term for any type of "malicious" program, using all sorts of tricky methods to get itself onto your computer. It will often pretend to be something else, like a piece of software you want, hidden in a file you've been sent or even appearing to be a warning from a virus checker.

Once it's on your computer and embedded into the memory, it can do anything from trying to capture your passwords and bank details, deleting important files or even allowing someone else to enter and take over your system.


A Trojan is a file that disguises itself as a legitimate file or program. Once run, they can destroy or leak your personal files to an outside source. Unlike a virus these cannot replicate or run themselves. Normally, you become infected through opening an infected email attachment or running an infected file from a floppy disk, CD or the internet.


Spyware is different from a virus because it doesn't delete files or stop your computer from working. Instead, it spies on you, collecting data like passwords, bank details or simply reporting what websites you've visited. Spyware runs silently in the background, using your computer's resources and your internet connection - making your computer run much slower than it usually does.

You can avoid Spyware by taking precautions when browsing the internet. If a pop-up appears on screen offering free stuff, don't click on it. Try to keep away from file-sharing programs as these are one of the biggest sources of spyware on the internet. What looks like a new song or program could actually be spyware in disguise.


Worms are programs that spread from system to system and are able to replicate themselves without the need for an infected host file; these normally reside in Word or Excel files. Once they're on a computer they'll release an infected document onto that system. When the file is copied to another computer this in turn releases an infected file onto the new system.

Tips for preventing virus infections

It's a well-known fact that all computers are likely to become infected with a virus at some point. However, you can minimise the risk and reduce the damage a successful infection can cause by following the steps below:

  • Don't delay in getting internet security for your computer. It's much easier for a virus to find its way onto your computer without any protection.
  • Install reputable anti-virus software: There are a number of programs available to buy from a computer store, with some decent free programs available on the internet. Also, if you bought your computer from a store you may have been supplied with an anti-virus program as part of a software package.
  • Check for software updates on a weekly basis: Anti-virus software normally comes with a period of free updates which can range from 3 - 12 months. You'll need an internet connection to install the updates.
  • Run regular full system scans: Many virus checkers can be scheduled to run automatically on a certain day and time that's convenient to you
  • Set your security software to automatically scan emails and their attachments
  • Don't open emails from people you don't know, especially if it has an attachment. Disable the preview pane in your email program; some viruses exploit this feature and launch themselves without you running them.
  • Scan any files you download or receive on disc before running them. Only download from websites you can trust and run discs from reliable sources.
  • Be careful when using peer-to-peer file-sharing software. The files you're downloading may be infected or they may not be what they appear to be.

Think your computer is infected?

Your security software will be able to protect you most of the time but if you find that something has slipped through the net and infected your computer, you can use anti-virus software to remove it or alternatively you can deal with it using Safe Mode.

  • First, scan the computer with an up-to-date security package such as Norton 360, Kaspersky, McAfee or Microsoft Security Essentials. Note: Disconnect from the internet before you start the scan. Also, try to run software that is more specific, for example, Malwarebytes or McAfee Stinger.
  • If you still have problems, you might want to use System Restore to go back in time to when your computer was working properly
  • If a program or message is preventing you from accessing your computer, you'll need to start it up in Safe Mode with networking

Safe Mode with networking

repair your computer windows
  • Turn on your computer and as it boots up, repeatedly tap the F8 key until the Advanced Boot Options displays (Note: You might need to press another F key for this option, depending on the computer make/model)
  • Your screen will look similar to the above image; use the arrow keys to highlight Safe Mode with Networking and press Enter
  • If you have access to your computer after the last step, run a scan using your security package
  • If the security software won't run or you don't have any installed, download and scan your files with anti-malware/spyware software
  • If you can't connect to the internet, try downloading your software from another computer and copying the installation files onto a USB/memory stick to install onto the infected computer.

TIP: Some malware will recognise anti-malware /spyware software and attempt to stop it running or installing. If you discover this is happening, disconnect your computer from the internet and try renaming the file before you copy it onto the computer or once it's installed.

If you can access the internet, search reputable anti-virus forums such as Symantec Communities to see if anyone has a solution to fixing your particular problem. If you're unsuccessful in removing the infection or you can't access the computer in Safe Mode you'll need to seek specialist help. If needed, our Knowhow team offer the following service:

Updated On:

Nov 22, 2013

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