In computer security, a virus
is a self-replicating program that spreads by inserting
copies of itself into another program. A computer virus
acts almost like a biological virus, which spreads by
inserting itself into living cells. Viruses are one of
several types of other malware. Other types of malware
include worms, trojans,
spyware, and other sorts of malware. However viruses are
less common today than network-borne worms, which self-replicate
at alarming rates.
There are many different types of viruses.
The most common are file, macro, and script viruses. Some
older types of viruses (which are almost nonexistent as
of this time of writing) are boot viruses.
More complex types of viruses are polymorphic
and metamorphic viruses. Polymorphic viruses
infects files with an encrypted copy of itself, which
is decrypted by a decryption component. In the case of
polymorphic viruses, this decryption component is also
modified on each infection, making it almost impossible
to detect these threats using virus signatures. Anti-virus
software can detect these viruses by decrypting the virus
using an emulator, or by statistical pattern analysis
of the encrypted virus body.
Some polymorphic viruses employ polymorphic
code in a way that it slows down the mutation rate of
the virus. The advantage to using such slow polymorphic
code, is that is makes it more difficult for anti-virus
professionals to obtain representative samples of the
virus, because of bait files that are infected in one
run will typically contain identical or similar samples
of the virus. This makes it more likely that the detection
by a virus scanner will be unreliable, and that, the result
of this, some instances of the virus may be able to avoid
detection given enough time.
By far, the best way to protect against
computer viruses is to install an anti-virus software.
Remember, just because you have an anti-virus doesn't
mean you will be immune to everything out there on the
internet. You must regularly update the anti-virus software
in order for the anti-virus software to protect your against
the latest threats.
