Spyware can closely resemble computer viruses, but with some important differences. Many spyware programs install without the user's
knowledge or consent. In both cases, system instability commonly results.
A virus, however, replicates itself: it spreads copies of itself to other computers if it can. Spyware generally does not self-replicate.
Whereas a virus relies on users with poor security habits in order to spread, and spreads so far as possible in an unobtrusive way (in
order to avoid detection and removal), spyware usually relies on persuading ignorant or credulous users to download and install it by
offering some kind of bait. One typical spyware program targeted at children, for example, claims that:
A typical piece of spyware installs itself in such a way that it starts up every time the computer starts up (using CPU cycles and RAM,
and reducing stability), and runs at all times, monitoring Internet usage and delivering targeted advertising to the affected system.
It does not, however, attempt to replicate onto other computers - it functions as a parasite but not as an infection.
- He will explore the Internet with you as your very own friend and sidekick! He can talk, walk, joke, browse, search, e-mail, and
download like no other friend you've ever had! He even has the ability to compare prices on the products you love and help you save
money! Best of all, he's FREE!
A virus generally aims to carry a payload of some kind. This may do some some damage to the user's system (such as, for example, deleting
certain files), may make the machine vulnerable to further attacks by opening up a "back door", or may put the machine under the control
of malicious third parties for the purposes of spamming or denial of service attacks. The virus will in almost every case also seek to
replicate itself onto other computers. In other words, it functions not only as a parasite, but as an infection as well.
The damage caused by spyware, in contrast, usually occurs incidentally to the primary function of the program. Spyware generally does not
damage the user's data files; indeed (apart from the intentional privacy invasion and bandwidth theft), the overwhelming majority of
the harm inflicted by spyware comes about simply as an unintended by-product of the data-gathering or other primary purpose.
A virus does deliberate damage (to system software, or data, or both); spyware does accidental damage (usually only to the system software).
In general, neither one can damage the computer hardware itself. Certain special circumstances aside, in the worst case the user will need
to reformat the hard drive, reinstall the operating system and restore from backups. This can prove expensive in terms of repair costs,
lost time and productivity. Instances have occurred of owners of badly spyware-infected systems purchasing entire new computers in the belief
that an existing system "has become too slow."
Internet Security Basics
Adware, spyware and malware
The Danger of Spyware
Virtual private network