What are computer Viruses ?

Computer virus are malicious programs.

First thing, like animal viruses, they spread from one computer to the other without your consent.
Years ago, virus were infecting floppy disks and each computer using the disk would be infected.
Nowadays, viruses mainly spread using the Internet as a channel. The virus is usually hidden in an email, in a file such as picture, movie or music, in application files such as games or software. Finally, virus can also be hidden in web pages.
While virus can be anywhere, there are places which are safer than others. Just like normal life. If you visit only famous websites such as Amazon or Google, your laptop has much less chances to be infected by a virus. If you visit websites containing porn or illegal copies of music, movies and games, your computer has a lot more changes to be infected.
Some virus are just malicious because they infect computers, but they actually don't do anything wrong except pollutiong your systems.
However, since the last few years, most virus are really malicious. They take control of your computer which is used, without your consent and your knowledge, for illegal activities such as sending spam emails, DoS attacks, etc. Some viruses also steal your personnal informations. Finally, some viruses stole your personnal files, such as holiday pictures and the authors ask for money to recover the lost files.

How should you protect your laptop ?

The good news is that it is actually not more difficult to be protected against computer viruses than similar issues in normal life.
The guidelines are simple:

• Don't go to unsafe places (don't visit unsafe websites). Don't do illegal activities. Just as in normal life, this is the main recommendations to be safe. Users cannot see easily if a virus is hidden in a webpage, but it is quite easy to see if it is a place you would recommend to other people...
• Keep your operating systems updated. System updates improve the security on your computer.
• Install antivirus programs such as Antivir, AVG, Norton, Microsoft Live Essential, etc.