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What is a Virus ?
What is a Spyware ?
What is a Computer Worm ?
Antivirus Software
Vulnerability
Replication strategies
Recovery methods
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 A
computer worm is a self-replicating computer program. It uses a
network to send copies of itself to other nodes (computer terminals
on the network) and it may do so without any user intervention.
Unlike a virus, it does not need to attach itself to an existing
program. Worms always harm the network (if only by consuming
bandwidth), whereas viruses always infect or corrupt files on a
targeted computer.
Naming and history
The name worm comes from The Shockwave Rider, a science fiction
novel published in 1975 by John Brunner. Researchers John F Shoch
and Jon A Hupp of Xerox PARC chose the name in a paper published in
1982; The Worm Programs, Comm ACM, 25(3):172-180, 1982), and it has
since been widely adopted.
The first implementation of a worm was by these same two researchers
at Xerox PARC in 1978.[1] Shoch and Hupp originally designed the
worm to find idle processors on the network and assign them tasks,
sharing the processing load, and so improving the 'CPU cycle use
efficiency' across an entire network. They were self-limited so that
they would spread no farther than intended.[2]
Payloads
Many worms have been created which are only designed to spread, and
don't attempt to alter the systems they pass through. However, as
the Morris worm, and Mydoom showed, the network traffic and other
unintended effects can often cause major disruption. A "payload" is
code designed to do more than spread the worm - it might delete
files on a host system (eg the ExploreZip worm), encrypt files in a
cryptoviral extortion attack, or send documents via e-mail. A very
common payload for worms is to install a backdoor in the infected
computer to allow the creation of a "zombie" under control of the
worm author - Sobig and Mydoom are examples which created zombies.
Networks of such machines are often referred to as botnets and are
very commonly used by spam senders for sending junk email or to
cloak their website's address.[3] Spammers are therefore thought to
be a source of funding for the creation of such worms,[4][5] and
worm writers have been caught selling lists of IP addresses of
infected machines.[6] Others try to blackmail companies with
threatened DoS attacks.[7]]
Backdoors, however they may be installed, can be exploited by other
malware, including worms. Examples include Doomjuice, which spreads
using the backdoor opened by Mydoom, and at least one instance of
malware taking advantage of the rootkit backdoor installed by the
Sony/BMG DRM software utilized by millions of music CDs prior to
late 2005.
Worms with good intent
Beginning with the very first research into worms at Xerox PARC
there have been attempts to create useful worms. The Nachi family of
worms, for example, tried to download and install patches from
Microsoft's website to fix vulnerabilities in the host system — by
exploiting those same vulnerabilities. In practice, although this
may have made these systems more secure, it generated considerable
network traffic, rebooted the machine in the course of patching it,
and, most importantly, did its work without the consent of the
computer's owner or user.
Most security experts regard all worms as malware, whatever their
payload or their writers' intentions.
Protecting against dangerous computer worms Worms mainly spread by
exploiting vulger operating systems, or by tricking users to assist
them.
All vendors supply regular security updates[8] (see "Patch
Tuesday"), and if these are installed to a machine then the majority
of worms are unable to spread to it. If a vendor acknowledges a
vulnerability but has yet to release a security update to patch it,
a zero day exploit is possible. However, these are relatively rare.
Users need to be wary of opening unexpected email, and should not
run attached files or programs, or visit web sites that are linked
to such emails. However, as the ILOVEYOU worm showed, and as
phishing attacks become more efficient, tricking users will always
be possible.
Anti-virus and anti-spyware software are helpful, but must be kept
up-to-date with new pattern files at least every few days.
Ref.: wikipedia
GNU Free Documentation License
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