A computer virus is a program specially made to auto replicate and spread. It infects many computers, without a pre-agreement with the computer’s owner.
They spread by attaching to some programs like: .exe file, .com files, and recently to WORD, Excel, or even to HLP files. Some of the viruses can affect the boot sector of the HDD.
When an infected file is executed, or when the computer is started using an infected CD or diskette, the virus starts its work. Sometimes, the virus remains in the computer memory just to infect the next program to be run.
The dangerous viruses have the ability to execute some actions. Sometimes those actions are annoying (like the display of some response on a certain date and time, or as a feedback to an user action), or they can be very annoying – like slowing the computer performance. There are viruses that can cause a very big trouble, destroying files of data, documents or making the computer unusable.
First viruses started to appear few decades ago, but they begin to spread when the first PC’s were invented. In 1981, IBM promoted a personal computer, using the “new” processor, 8088, created by Intel. The prices were expensive, but the product was a real success. As a operating system, IBM bought MS-DOS from Microsoft. First versions of DOS were extremely compact and didn’t have an included security protocol.
After 5 years, in 1986 appeared the first reports indicating viral entities on IBM-PC’s. The virus was Brain, a boot virus. As a response to that, antivirus software is created. The first antivirus applications were extremely simple, like the viruses they had to deal. Nowadays, they are more complex in algorithms and code.
How does a virus spread?
The viruses’ provenience can be a great variety of sources. A virus can be transmitted in any way between computers, because it’s executable code.
Dataquest provided National Computer Security Association from the US with a study conceived in 1991, which pointed that 87% of the viruses spread trough infected diskettes. 43% of the infected diskettes were brought by home.
Almost 71% of infections appeared in enterprises, which used networks that increased the spread of the viruses. The risk of infecting in a network is much higher. The source for 7% of the viruses was BBS.
6% of the infections were made by the demo diskettes or by diskettes that contained archives.
Like you read before, some viruses can be annoying and the other extremely dangerous.
The happiest case is that when the viruses increase the file’s dimensions and decrease the response speed, affecting your computer performance.
Some of the viruses try just to spread, not to affect your computer, so they don’t intentionally produce damages.
Anyway, there is a possibility that they interact with another programs or with the HDD and to slow or stop the system.
The dangerous ones can modify and destroy data, or they can erase files, or worst, format your HDD.
The initiated persons in this domain can’t probably have difficulties in diagnosing an infected system.
Viruses can spread just as long as they are not tracked down. This is the reason why most of the viruses don’t show their presence in the system. Only the antivirus software can detect them.