With the advent of the Internet, almost every computer has the potential to be connected to almost every other computer. Whilst this may be a very good thing for the exchange of information, it's also a very good thing for the exchange of mischief, as not every single computer user is a fine, upstanding, pillar-of-the-community type. Many people reading this will already have found themselves on the receiving end of a computer virus¹ or a Trojan Horse - a form of virus which allows another person to remotely take control of the affected computer.

Can I completely eliminate these nasties from my computer?

In a word, no. Just as it is impossible to completely prevent someone from breaking into your house or car if they are really determined, there will always be hackers and viruses trying to get themselves onto your computer. But in the same way that you can take steps to lessen the threat of burglary and theft, you can make it more difficult for them to succesfully invade your computer.

Some may say that the most obvious thing you can do to avoid viruses is to buy an Apple computer. Microsoft operating systems currently have a bad reputation where security is concerned, and the fact that by far the majority of computers today use a Windows operating system makes them very juicy targets for virus writers. Apple operating systems are, comparitavely speaking, so few and far between that it hardly seems worthwhile writing a virus which affect such a small number of a people. For that very reason, this entry will be aimed mostly at users of Windows operating systems.

So what can I do to protect myself?

What follows is a list of simple, common sense practices, none of which are beyond the skill of the average computer user. In other words, you don't have to be a full-fledged, card-carrying geek to keep your computer safe and healthy.

1. Update your system regularly

No operating system is perfect², and every so often flaws and holes are discovered which could allow someone to get into, or hack your system. Sometimes these holes are discovered by Microsoft, sometimes by people who see it as their mission to find fault with everything Microsoft does. Whenever one of these holes is discovered, Microsoft will construct a patch to block any hackers from using the hole to get at your computer. Fortunately, Microsoft has built into Windows an easy way to get these patches and download them onto your computer.

Open a browser window, first connecting to the Internet if you are on a dial-up connection. At the top you should find the toolbar. This is the part of the window which says things like 'File', 'Edit', 'View', etc. Click on 'Tools' and a menu will appear listing several options. Clicking on 'Windows update' will take you directly to the section of the Microsoft website where you can download any patches which may be necessary. Once there you will see a link which says 'Scan for updates'. By clicking on this link Microsoft will remotely examine your operating system and check it for security holes. Usually there will be nothing more than various tools to help you convert from one currency to another, or to enable your browser to read (for instance) Russian alphabet characters, but every so often you will see the words 'Critical update'. When that notice appears, it means that a serious security flaw has been found and a patch devised. These should always be downloaded and installed on your computer.

Much more rarely you will see the words 'Service Pack'. A service pack is rather like a major overhaul for your operating system. It includes all of the critical updates since the last service pack (or the inception of the operating system) plus several tweaks to help your system run more smoothly). If you've been regularly updating your system you won't need most of the service pack, which is why Microsoft will have two versions - 'Full' and 'Express'. The express version will check your system and only download those parts of the service pack you really need. To give you an idea of why it's good to have all the updates already, the express version of the last service pack for Windows XP was an 11MB download whereas the full pack weighed in at a hefty 140MB. That could take you the best part of a day to download on a dial-up connection.

How often should you update? Some people advocate doing it daily, but generally it's ok to check for updates on a weekly basis. More recent Windows systems such as XP will even download and install updates for you automatically, although it's probably best to do it yourself, particularly if you doubt that you'll ever receive an email in Russian.

2. Get some good anti-virus software

Although there are free anti-virus programmes available for download, and even online virus checkers, generally speaking, good anti-virus software has to bought and, like your operating system, regularly updated. The two most common anti-virus software packages are those from MacAfee, and Norton Anti-Virus from Symantec. A good free online virus checker is Trend Micro's House Call or Comparite.

3. Turn off File Sharing

This is one which many people find impossible to do, because it is File Sharing which allows them to download mp3's from the likes of Napster and AudioGalaxy. If you never use any file sharing services, then it's easy to turn off this capability. In Windows 95/98/Me, open the Control Panel by going to your desktop and opening 'My Computer', then opening 'Control Panel'. Find the icon for 'Network', double click on it, and a window with three tabs will appear; choose the one marked 'Configuration' and toward the bottom you'll see a button marked 'File and print sharing'. Clicking on that will bring up a further window with two check boxes - one marked 'I want to be able to give others access to my files' and the other 'I want to be able to allow others to print to my printer(s)'. Make sure both of those boxes are unchecked.

In Windows NT/2000/XP, click on 'Start', and open the Control Panel. Click on 'Network and Internet Connections', then 'Network Connections', which should take you to a window which shows details of your Internet connection. Right click on the icon and select 'Properties'. A window will appear with three tabs - select the one which says 'General, and uncheck the box for 'File and Print Sharing for Microsoft Networks'.

4. Get a firewall

This one is particularly important for those on broadband connections³ which are 'always on'. A firewall restricts incoming and outgoing traffic on your computer, and can render your computer invisible to the outside world. If a hacker should try to gain access to your machine, the firewall will prevent them from getting inside. Windows XP comes with a built in firewall, but it only does half the job as it only restricts incoming traffic. Some programs could send information out which you'd rather keep in, such as your surfing habits, or passwords. Furthermore, the XP firewall is turned off by default. To turn it on, follow the instructions above for turning off file-sharing, but instead of the 'General' tab, choose the one marked 'Advanced', and check the box which says 'Protect my computer and network by limiting or preventing access to this computer from the Internet'.

A much better solution, particularly if your operating system doesn't have its own firewall is to download and install one. By far the best one around is Zone Alarm, and although there is a version which you can buy, the free version is more than adequate for most home users. Like your system and your anti-virus software, a firewall also needs updating from time to time, and the supplier will notify you when it's necessary.

5. Encrypt sensitive files

Even though you may have taken all the above precautions, there is still a remote chance that a hacker could gain access to your computer. In that event, they would not find much of any interest if your files were encrypted. The most well known free encryption software is Pretty Good Privacy or PGP. PGP will scramble your files to such an extent that even MI5 or the CIA will have to throw everything they've got at them if they want to read about your plans to... well, let's not go into that.

6. Backup your files regularly

There are two ways of backing up important files and information - on, or off your computer. Windows has a backup feature which will allow you to make copies of files and store them in a backup, or .bac file. However, this won't be much good to you if a virus has stopped your computer dead in its tracks or if your entire hard disc crashes. A much better idea is to store anything you don't want to lose either on floppy discs, on a Zip drive, in an online storage facility, or, as cd burners come down in price and become much more common, on a cd-rom.

It shouldn't really be necessary to backup absolutely everything on your hard disc - you don't need to backup the operating system for instance, as long as you still have the 'System restore' disc that came with your computer. Only backup those files which you would regret losing, or which you know for sure that you couldn't get again.

7. Don't open suspect email attachments

This is how most viruses find their way onto computers, and they often come from friends who have themselves been unwittingly infected. Never, never, ever open an attachment if you don't recognise the name of the sender, or if the attachment has .exe, .bat, or .doc ⁴ at the end of its name. Sometimes viruses can be disguised by putting multiple file extensions on them, but it's always the last one which the computer uses to identify the file type and that's the one you should take note of. For instance, you may receive an email with an attachment called 'My holiday pic.jpg.gif.exe'. That attachment will not be a picture of your friend on a beach somewhere.

Conversly, you should be responsible about sending attachments. Don't just tag the attachment onto a blank email - write some kind of message which the recipient will recognise as being from you rather than from the warped mind of a virus writer. Personalise it in some way so that they can see it's definately you who is sending the email, like mentioning the last time you spoke to each other, or something from your last email. Do the same with the subject - virus writers know that subject lines such as 'This is really funny' or 'Here's my girlfriend naked' will get a lot of people to open attachments without thinking first. That's precisely how the 'Anna Kournikova' virus managed to spread around the world in no time flat.

8. Turn off the 'preview pane' in Outlook Express

Some of the more sinister viruses don't even need to be run as an attachment - they can be coded into an email and can infect your machine simply by opening the email. If you are using Outlook Express and have the preview pane⁵ enabled, you can easily allow such a virus onto your computer because the preview pane automatically opens the first email in your inbox. To disable the preview pane open Outlook Express, click on 'View' in the toolbar, then selct 'Layout' from the drop-down menu. Uncheck the box which says 'Show preview pane'. From that point on you will simply be shown your inbox and you can choose which emails to open and which to delete.

9. Use web-based email

You can further eliminate the chances of a virus infecting your computer by opening an account(s) with one of the many free web-based email such as Yahoo!, Hotmail, or Excite. With web-based mail you don't actually download the emails to your machine, you view each one as a web page, so if a virus is going to infect a machine it's going to be theirs not yours⁶.

10. Don't use your address book

This tip is not so much to help you keep your own machine secure but those of all your friends should yours become infected.

So, you've followed all of the above tips, but somehow your machine has been infected by a virus - maybe you forgot to update your anti-virus software or you inadverdantly opened an attachment which you thought was something legitimate from one a friend. One of the first things most viruses do is to find the address book in your email software and send itself to every address it finds there. However, if the book is empty it stops at your computer, it can go no further. But where do you keep your addresses? In a text editor such as Microsoft Notepad. Simply write the names and email addresses of all your contacts in a Notepad file and save it to the 'My Documents' folder, naming it whatever takes your fancy. Whenever you need an address you can open the file and then copy and paste it into the address field of the email. It's a little more lengthy than clicking on a name in your address book, but if it halts the progress of a virus it's worth the effort.

I've done all that and I'm feeling quite smug

Good for you! Be happy that you've taken measures to keep your computer⁷ running smoothly. Don't ever get complacent though - those pesky hackers and virus writers are always devising new ways to do get at your machine, and they rely upon computer users letting down their guard.