Helpful Hint

Computer security has become a serious issue as use of the Internet has grown so strongly. The Internet is now the main way for malicious computer programs, files and messages (now commonly called malware) to be exchanged. You computer is now exposed to threats from outside such as computer viruses, trojans, hoax letters and denial-of-service attacks.

Computer viruses behave rather like the natural kind - they spread from one computer to another, and usually cause misery. When this article was first written few users encountered them, but increasing use of the Internet by individuals, charities and other organisations as well as by businesses has made them much more commonplace. There is no doubt that they have become a serious nuisance as the originators of viruses find new ways of spreading them and new ways to hide them from anti-virus products. The phrase "computer virus" is usually reserved for programs that have the ability to replicate and propagate and the ability to cause damage, and they are one of many kinds of malicious matter to be found in computer systems and networks.

Trojans are programs that lurk unnoticed in your computers, usually disguised as or cloaked in apparently useful files. By themselves they aren't able to replicate or propagate, but they are usually loaded from the Net and installed by users who do not realise that they are wolves in sheep's clothing. Once installed, they may corrupt your computer's files insidiously, or offer control of your computer to unscrupulous users on the other side of the world.

Protection has now become vital if you exchange computer files or messages with others (either by disk or by a computer network, especially the Internet) or if your computer any kind of Internet connection. Provided you are properly protected, you needn't fear them too much - many users will suffer little more than inconvenience and with a little care you can keep them away. Even if your computer catches a virus, you can still eradicate it and usually repair the damage.

What are they, and what do they do?

Computer viruses are maliciously-designed programs which attach themselves to innocent programs and documents, make copies of themselves and interfere with the normal operation of computers. The interference can be anything from mild (displaying a silly message on your screen) to severe (wiping all the data from your hard disk, or exposing passwords, private data and control of your computer to malicious Internet users). Some viruses can stop your computer working altogether, but those are rare.

Spreading a computer virus or other malicious computer matter deliberately is a criminal offence.

How do they spread?

In the past viruses were often passed between computers on floppy disks. This still happens but now the commonest method of spreading is by programs embedded in documents transmitted by electronic mail. The documents are usually those managed by Microsoft Word, which has a macro language with almost limitless capabilities to alter data on your computer's disk or to run other programs in improper ways. Other infected or disguised programs that would previously have been copied using floppy disks are now passed around computer networks, including the Internet.

When a virus is run, it often disguises itself in another program, document or disk, which might then be sent to another computer. A very rapid spread can be achieved by viruses which quietly send copies of themselves by e-mail to all the users in your computer's address book!

How do I avoid "catching" a virus or passing it on?

Above all, don't worry. Just follow these rules:

• Install Anti-Virus software! This has now become essential for anyone using the Internet as there is now so much malicious matter about. It has become likely that someone you know has been an unwitting victim of an attack and may now be an unwitting accomplice in attacking you.
• Keep your Anti Virus software up to date. New versions of malicious matter appear every day.
• If you have Microsoft Windows, tighten up your security precautions now! Windows 95, 98 and Me are very vulnerable as delivered.
• If you spend much time connected to the Internet - and especially if you have a permanent connection, perhaps using a cable modem - install additional protective software to stop your computer from being "hijacked" into malicious activity.
• Be suspicious of all documents coming from outside your computer. Viruses don't usually advertise themselves and innocent users can easily pass them on. Use a document viewer such as Microsoft's Word Viewer, available from http://www.microsoft.com to view a document from an outside source.
• Never run or install a program from a disk or from a computer network unless you know the source can be trusted. Be very suspicious of program disks copied by your friends and colleagues. Even if they don't contain a virus, they might be illegal copies.
• Whenever possible, keep floppy disks and other writeable disks write-protected. Your program disks should be protected before you install them. If they're not, then protect them and keep them protected. Keep data disks protected until you need to save data onto them.
• Only start your computer from a floppy disk if you really need to. Make sure that you are using a disk you can trust.
• Always remove floppy disks from your computer as soon as you have finished with them.

How do I know if my computer has a virus?

One way is to discover your computer behaving strangely (displaying strange messages, playing tricks with your keyboard, corrupting files ....). If this happens some damage has been done, and you must immediately take steps to eradicate the virus and repair the damage. A safer way is to scan your computer's disks regularly using a program designed to detect viruses. Even better, use virus protection software that checks documents and programs when you try to use them, and stops them from being used unsafely. Without regular scanning or checking, a virus may lurk undetected, silently reproducing itself, until it carries out its damage. Viruses don't usually cause damage immediately - that would make them too easy to detect!

If you discover that your computer has been affected by a virus, make sure you tell everybody with whom you share files. If you don't, other people might hold you responsible for any damage they suffer. If you discover a virus in something you have received, tell the sender immediately to stop him sending it to other users.

How do I protect my system from virus damage?

BACK UP YOUR DATA AND PROGRAMS! Copy the contents of your computer's hard disk to floppy disks or (much better) a magnetic tape cartridge or high-capacity removable disk. Do it regularly. Keep enough generations of backup to protect against failure while the backup is happening. This will also protect you from damage arising from other causes, such as hardware breakdown, careless operations and malicious attacks. We'll cover backups in a future hint.

If you have Microsoft Windows 95, 98 or Me, adjust the Internet Explorer security settings so that script execution is always prompted, even on trusted sites. Adjust Outlook Express settings to use the most secure Internet settings. Change the Windows Explorer view options so that, for all folders, file extensions are never hidden and all files, including hidden and system files, are always shown.

HIDE YOUR PRIVATE DATA! Keep it in parts of your system which are not exposed to the Internet. If necessary, use Firewall software to protect your computers from intrusion by other users, or encrypt your data so that it cannot be read even if it is stolen.

CHANGE YOUR PASSWORDS FREQUENTLY! Some viruses can allow Internet users to see your passwords unencrypted.

USE ANTI-VIRUS SOFTWARE! In the past this was needed only by a minority of users. In these days of networking, e-mail and web browsing, it's only the minority who can do without. There are many reputable providers of suitable software.

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