Editing Computer worm (section)

{{Short description|Self-replicating malware program}}
{{About|coding of a worm|the data storage device|write once read many|other uses|Worm (disambiguation)}}
{{Distinguish|Computer virus}}
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[[File:Virus Blaster.jpg|thumb|right|325px|[[Hex dump]] of the [[Blaster (computer worm)|Blaster worm]], showing a message left for [[Microsoft]] [[CEO]] [[Bill Gates]] by the worm's creator]]
[[File:Conficker.svg|thumb|Spread of [[Conficker worm]]]]
A '''computer worm''' is a standalone [[malware]] [[computer program]] that replicates itself in order to spread to other computers.<ref>{{cite web|last=Barwise|first=Mike|title=What is an internet worm?|url=http://www.bbc.co.uk/webwise/guides/internet-worms|publisher=BBC|access-date=9 September 2010|archive-url=https://web.archive.org/web/20150324073759/http://www.bbc.co.uk/webwise/guides/internet-worms|archive-date=2015-03-24}}</ref> It often uses a [[computer network]] to spread itself, relying on security failures on the target computer to access it. It will use this machine as a host to scan and infect other computers. When these new worm-invaded computers are controlled, the worm will continue to scan and infect other computers using these computers as hosts, and this behaviour will continue.<ref>{{Cite journal|last1=Zhang|first1=Changwang|last2=Zhou|first2=Shi|last3=Chain|first3=Benjamin M.|date=2015-05-15|title=Hybrid Epidemics—A Case Study on Computer Worm Conficker|journal=PLOS ONE|volume=10|issue=5|pages=e0127478|doi=10.1371/journal.pone.0127478|pmid=25978309|pmc=4433115|arxiv=1406.6046|bibcode=2015PLoSO..1027478Z|issn=1932-6203|doi-access=free}}</ref> Computer worms use [[recursion (computer science)|recursive methods]] to copy themselves without host programs and distribute themselves based on exploiting the advantages of [[exponential growth]], thus controlling and infecting more and more computers in a short time.<ref>{{Cite journal|last=Marion|first=Jean-Yves|date=2012-07-28|title=From Turing machines to computer viruses|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=370|issue=1971|pages=3319–3339|doi=10.1098/rsta.2011.0332|pmid=22711861|bibcode=2012RSPTA.370.3319M|issn=1364-503X|doi-access=free}}</ref> Worms almost always cause at least some harm to the network, even if only by consuming [[bandwidth (computing)|bandwidth]], whereas [[computer virus|viruses]] almost always corrupt or modify files on a targeted computer.

Many worms are designed only to spread, and do not attempt to change the systems they pass through. However, as the [[Morris worm]] and [[Mydoom]] showed, even these "payload-free" worms can cause major disruption by increasing network traffic and other unintended effects.