Is your computer is running slowly and seems to be at the edge. You may have a virus on your computer. So, let us see, what is a virus? what it can do for your computer? How can you do protect your computer from it?

The virus is a malicious program which replicates itself through your computer without asking you or takes permission from you. This program can infect your files and make it malfunctioned. For example, you may open a Microsoft word file and see it failed to open. Assuming that the cause of this failure is a virus, and then you will likely to see other files is malfunctioned as soon as one file is failed due to a virus on your computer.

In essential, a virus is large collection of instructions attached to one of your programs. These instructions can be getting from different sources such as browsers when you open the internet, a link in email, floppy disk, flash memory, or others. When one of these programs is opened, these instructions are executed along with the original program you opened and load itself in the memory, and then it can write itself to other files in the computer.

In fact, there are two strategies the virus can infect with. The first one is called Nonresident strategy. In this type of infection, the virus looks for other files and resources to infect only on the local computer. In the second strategy, which is called, Resident strategy, the virus looks for other hosts to infect if it is connected to a local network.

The most important is how to prevent these viruses from your computer. The common technique is to install an anti-virus software on your computer. This software works by detecting viruses on your computer. It has many techniques to detect that there is an existing virus according to software vendor. It can detect it based on signature in the file it scan. A signature is a certain pattern it looks for and if exists then it decides that a virus exists. Every sofware that uses thuis technique has a database of this signatures which represents the most common viruses. Some anti-virus sotware also detect by looking for the behaviour of the file being opened which is called heuristic detection .

A second technique to prevent your computer from viruses is to backup your data. If some files is infected on your computer, you will find some copies of your data. You can store it, for example on CD, or DVD.

An important notice to consider when using anti-virus software is that the signatures used by these programs are updated regularly. this is because new attacks are discovered every a certain period. thus you must be confirmed that the software is updated every time it is opened. if it is expired and still installed, it will not be safe because the database may not be updated which means that newer types of attacks have not been discovered yet.