The short answer is No, it will usually not just slow down your computer but will also do some damage. The long answer is that, whether it just slows down your system or breaks it and how much it breaks it, really depends on the type and the sophistication of the virus that your computer gets infected with.

There are many different types of virus, all serving their own purpose. Adware is a type of a virus that causes your computer to display annoying pop-up ads to get you to buy something. Spyware is another type of virus that infiltrates your computer and silently spies on everything you do so that it can send valuable information such as social security and credit card numbers to its owner. Its presence also makes your computer a little slower than usual. And then there are the other types such as trojans, worms, etc.., that get into your computer and corrupt personal and system files. The corruption of system files causes your computer to act erratically. Depending on the severity of corruption and the importance of files corrupted, you can either escape with some error messages and a slower computer, or have your system be put in a completely irreparable state.

As you can see, having your PC be infected with a virus of any kind can be quite a nuisance unless you are protected by a good ant-virus program. A good anti-virus program can not only find and remove existing viruses on your PC, but it can also help you stay protected from future attacks.

Alex Shtraykher is a computer science major. For unbiased expert anti-virus software reviews and other useful tips on how to keep your pc safe, visit: http://www.squidoo.com/anti-virus-software or go to http://www.squidoo.com/adware_software