It is weird right? Computer viruses can never be beneficial! I thought about it too but don’t worry you are in safe hands. After writing this article I had to do a compulsory medical check up. I know you are pondering and wondering how on earth can viruses be beneficial? Chill, technology is advancing. You might be ordering for tons of computer viruses on Amazon someday. Maybe after reading this article you might find your self doing something you thought you could do in your dream-not just downloading for free, but buying a virus code for your sweet pink lap top. For safety reasons, my computer guru friends and I are not going to give links on getting these codes, but just for research and development purposes, we are going to discuss these ‘good’ computer viruses.
No doubt 99.99999% of computer viruses are dangerous and too wicked as they have the powers to make our lives miserable. Computer virus which is best defined as a self-replicating program that can infect other programs by modifying them in their environment is too wicked to be beneficial. I know, even my grand mom can testify to that. Ever since I lectured her on viruses, she has been blaming computer viruses for virtually everything ranging from low batteries to no network coverage. However, as I stated earlier ‘chill’. You are about to discover an amazing fact about computer viruses. After coming across a brilliant and long-life work of Dr. Cohen in his Cohen88 master piece, my mentality about computer viruses changed. Below are lists of some computer viruses that can actually be beneficial and good.

1. The ‘Maintenance’ Virus: This virus was first described by Dr. Fred Cohen in [Cohen91]. The idea consists of a self–contained program, which spawns copies of itself across the different machines in a network (thus acting more like a worm) and performing some maintenance tasks on those machines like deleting temporary files, deleting them and so on. A similar idea can be implemented in memory as multiple concurrent processes, instead of programs in files spreading across the network.
2. The ‘Disk Encryption’ Virus: This virus has been published by Mark Ludwig—author of two books and a newsletter on virus writing, and of several real viruses, variants of many of which are spreading in the real world, causing real damage. The idea is to write a boot sector virus, which encrypts the disks it infects with a strong encryption algorithm (IDEA in this particular case) and a user–supplied password, thus ensuring the privacy of the user's data. Unfortunately, this idea is just as flawed as the previous ones.
3. The ‘File Compressor’ Virus: This is one of the oldest ideas for "beneficial" viruses. It is first mentioned in Dr. Cohen's original work [Cohen84]. The idea consists of creating a self–replicating program, which will compress the files it infects, before attaching itself to them. Such a program is particularly easy to implement as a shell script for Unix, but it is perfectly doable for the PC too. And it has already been done—there is a family of MS–DOS viruses, called Cruncher, which appends itself to the executable files, then compresses the infected file using Lempel–Zev–Huffman compression, and then prepares a small de-compressor which would decompress the file in memory at runtime.
4. The ‘Xerox PARC’ worm: In 1982, two researchers from the Xerox Palo Alto Research Centre created a "distributed computation" [Shoch]. This was a program written in BCPL for Xerox workstations, which consisted of several segments, each segment running on a workstation connected to a local–area network. The program was able to determine which machines were idle and to transfer a segment to them, thus expanding itself. Additionally, each segment could use the workstation it was running on for some useful task. In particular, during the experiments mentioned above, the segments were performing partial computations for animation purposes, using the idle machines on the network.
5. The ‘Anti-Virus’ Virus: This last example of beneficial self–replicating is the most successful one. Implementations of it are widely used by several anti–virus companies in their products. Consider a company that has several hundreds, even thousands of PCs, all networked together in a LAN. The company also takes the virus problem seriously, and insists that each and every one of these PCs must be running the latest version of some particular virus scanner, before it is allowed to access the network. Let us ignore for a moment whether the decision to rely on a scanner for virus protection is wise or not. Even if the company uses some other kinds of defence (integrity checking, monitoring, access control, and so on), a well thought out scheme for anti–virus defence should contain a scanner as one of the lines of protection, although possibly not the most important one.