A computer virus is a malicious piece of code that most commonly affects the system files or program files within your PC. A virus has the ability to infect various types of files with its executable code and severe viruses can also affect many other parts of your system by latching on to other programs and wreaking havoc.
Files vulnerable to attack also include files from the boot sector, which must be present and in full working order for the initial boot up or start-up process to take place. (If this boot sector is corrupted, often your PC will not turn on at all.)
Boot sector viruses
As mentioned above, Boot sector viruses are designed to attack important start-up files, altering or sometimes even deleting these files that the system needs to power up the PC.
A boot sector virus spreads by creating copies of itself and then scattering those copies throughout various locations on your hard drive. In severe cases boot sector viruses can leave your system completely inoperable, forcing a complete reformat of your hard drive in order to repair the damage caused.
If you are having problems loading up your PC and you suspect that you may have a boot sector virus present on your system, you should consult a virus removal specialist immediately to arrange for your PC to be thoroughly cleaned. The faster you act, the better the chance you will have of avoiding any irreparable damage to your PC.
A multipartite virus (also known as a multi-part virus), is a virus which simultaneously attempts to attack both the program files on the computer and the boot sector. The virus first gains access to and infects the boot sector before moving on to infect other system files. These system files then infect other program files and the virus is spread to other areas of your system.
Multipartite viruses are very dangerous and if all segments of the virus are not fully eradicated upon first discovery, it is capable of infecting your entire system again and again over time.
Whatever the type of virus, all viruses are effectively just software programs and have many of the same characteristics as safe, legitimate, trustworthy programs that you use on a daily basis. The only difference is that these malicious software programs are created specifically to interfere with the operation of your PC or to damage (or even delete) important or irreplaceable data and documents.