Computer virus

From Saferpedia

The virus is a software able to auto-replicate itself and infect the host computer. A virus may spread only from one computer to another as an executable. Viruses may increase their chances to spread to other computers by infecting shared files.

History

Creeper virus was detected for the first time on ARPANET the internet precursor on early 1970s. Creeper was an experimental software capable to auto-replicate written by Bob Thomas at BBN Technologies in 1971. Creeper used ARPANET to infect DEC PDP-10 computers running with TENEX OS. Creeper soon auto-replicated and got control of computer's management system and displayed the message "I’m the creeper, catch me if you can!". To remove Creeper was created Reaper software that managed to delete it.

The first virus that was outside a single computer or outside the lab where it was created is "Rothar Jr.". It was written in 1981 by Richard Skrenta and it auto attached to the Apple DOS 3.3 OS and spread trough floppy. This virus created as a practical joke by Skrenta during high school, was injected in a game on a floppy. On the 50th use the Elk Cloner virus would be activated displaying a short poem starting with Elk Cloner: The program with a personality”.

The first computer virus "in the wild" was a virus in the boot sector nicknamed (c)Brain, created in 1986 by Farooq Alvi brothers from Lahore, Pakistan.

Infection strategies

To auto-replicate a virus must be allowed to execute a code and to write in the memory. That's the reason why many viruses are attached to executable legal files.

Viruses can be divided in two base categories according to their behavior when executed:

Non resident viruses are viruses that search immediately for a new host once they've been executed infecting their hosts;
Resident viruses, are viruses that don't search for hosts once they're launched. The virus remains active in the background and infects new hosts when infected files are transferred.