There is no really a reason why a hacker should invade your computer, but you do need to protect it against viruses.

Computer viruses come in many different forms and have many different effects. They can just be annoying - for example displaying a message on the screen every time you press a certain key combination - or they can be downright destructive - deleting all the data on your hard drive. The more you use the Internet, the more careful you should be. The first way to protect your computer is to make sure that you download files only from reputable and well - known sources. However, this is not foolproof and you should also install a virus protector. Once loaded, every time you download a file from the Internet, the software will check it and repair it if necessary.

Viruses are tiny programs that hide inside other executable (.exe) files and macros. They are not contained within pictures or sound files. The main rules of thumb is that they are only contained within files that need a run command. The way they work varies, but generally they lie dormant on your computer until they are activated by a particular trigger: pressing the enter key a certain number of times, or using the computer at a certain time or on a certain date, for example. Not many viruses will cause major damage as any that do are quite easily detected and will be destroyed quickly before they are passed on. However, some can make your life very difficult - destroying the content of files, for example - and need to be avoided.

There are many ways to tell if you have a virus on your system. The most common one is that if you begin to notice that program take longer to start up or in some cases do no start at all. If this happens, then you should check that you have the latest version of your anti - virus software and then run a check on all files. The programs that are causing the problem should be removed and re- installed if a virus is found.

If you start up your computer and the screen displays nothing but a message saying 'MISSING OPERATING SYSTEM', it could mean that a virus had attacked your start up files. With most anti -virus software you should be able to create a disk called a repair disk. You boot up your computer using the repair disk, then run your virus checker.

Finally, if you see the message, ' INVALID DRIVE SPECIFICATION' when you start your computer , then I am afraid that unless you have a relatively new and clean backup you have lost everything on your computer. This message means that your computer's hard drive has been cleaned of ll data and become corrupt. The only way to rectify this is to reinstall all your programs and files.