What is a Polymorphic Virus?

Mary McMahon
Mary McMahon

A polymorphic virus is a computer virus which is capable of mutating itself when it replicates, making it more difficult to identify with ordinary antivirus software. To effectively find such viruses, antivirus software needs to have more complex algorithms available to help it identify distinctive patterns which can betray the presence of a virus even when the code behind the virus is not known to the software. Such software tends to be more expensive, reflecting the additional effort required during development and updates to make the software functional.

Polymorphic viruses can operate in different ways.
Polymorphic viruses can operate in different ways.

The first known polymorphic virus was developed in 1990, in the early days of the Internet, illustrating the fact that virus creators have always been ahead of the curve when it comes to developing malicious code. These viruses operate with the assistance of an encryption engine which changes with each virus replication; this keeps the encrypted virus functional, while still hiding the virus from the computer it infects and allowing the virus to slip through security systems which are designed to prevent malicious code from entering or exiting a network.

Infection with a polymorphic virus can be a serious problem.
Infection with a polymorphic virus can be a serious problem.

Essentially, the virus creators have integrated a trait associated with viruses which infect humans into the design of their software, designed to infect computers. Human viruses are infamous for being able to mutate rapidly to avoid detection and prevent the buildup of immunities, and when a computer virus has a similar trait, the results can be unpleasant for computer users. It can be difficult to mount an adequate defense against a polymorphic virus, even with excellent antivirus software which has been designed to attempt to detect such viruses.

Polymorphic viruses can operate in different ways. Some mutate with each infection, making the virus extremely difficult to track. Others change with each generation. The speed of mutation is also highly variable. Some viruses mutate more slowly, which can make it easier to catch them, while others change very quickly. All of these variations, as a whole, make these viruses very diverse, which adds to the challenge of pinning them down.

Infection with a polymorphic virus can be a serious problem. While all computer viruses are designed to remain undetected for as long as possible, so that they can exact the maximum damage and increase their chances of infecting other computers, a polymorphic virus can linger undetected even on a system with antivirus software in place. People may also be lulled into thinking that their system is clean because they have such software and they update it regularly.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a EasyTechJunkie researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@KoiwiGal - There's actually a polymorphic virus like that, which I think of as one of the most famous of computer viruses. It hasn't done anything yet, but it could one day.

I can't remember all the details about what it's called, but it's an extremely successful computer virus that has infected a large majority of computers. A team was tracking it and they eventually realized it was polymorphic and very difficult to pin down. The person who made it went to a lot of trouble to hide it so it will probably be used for something eventually.

But, the point is, you've probably got it on your computer right now and don't even know it. And your workplace probably has it on all their computers as well. It's a scary notion.


@MrsPramm - Well, they generally are there for a reason. It's not just to corrupt your computer (although there are some that just do that. There are no shortage of bad people in the world). Mostly the purpose of a virus is to do something to profit the person who made it. They might gather information about you (either relatively harmless stuff about where you shop, or much more harmful things like your passwords or credit card number). They might be trying to show you ads. They might be trying to get into your email so they can show ads to all your friends.

Once a virus has infected your computer the possibilities are endless. Some do nothing at all. Even polymorphic viruses. They might just be someone wanting to see how far they can spread themselves.


@anon66397 - I've never been able to understand the mindset of people who make malicious code like this. I mean, I kind of get it if it's a teenager trying to feel like a tough guy. But even then it's ridiculous. Who are all these people who send their days trying to inflict harm on people?

It can be so difficult to remove a computer virus and it's almost always just grandparents and other people without much experience who get them. I just don't see the point.


wow that's cool. It will probably end up being the only type of virus considered a virus.


The people who write this malicious code should be caught and prosecuted as terrorists.

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