A DoS attack is
the type of attack when a massive amount of requests is sent to a
specific target from one or several hosts. When a target reaches
its capacity of handling such requests, it becomes incapable of
answering all the requests it gets. So if a DoS attack is done by
a trojan, that continuously sends massive amount of requests to a
target (web, IRC server or a selected IP address), a target is
kept busy processing only the requests sent by a trojan and
requests coming from other sources are not processed at all or
are processed with delays.
DoS attacks become quite popular nowdays as they are in many
cases quite effective. For example in 2002 there was a DoS attack
on a few IRC servers and many users were unable to connect to
these servers. Also in 2002 there was an attack on a few big
websites and that disrupted normal communications to those sites
and caused losses to the companies who owned them.
Some worms perform a so-called 'political' DoS attack. For
example Yaha worm tries to DoS the Pakistanian government
website. Some trojans and worms try to DoS Microsoft's website.
Alexey Podrezov, July 14th, 2003;
Alexey Podrezov, May 24th, 2004;