This type of malicious program is designed to conduct a DoS attack from an infected computer on a pre-defined address.
Essentially, a DoS attack involves sending numerous requests to the victim machine; this leads to a denial of service if the computer under attack does not have sufficient resources to process all the incoming requests.
In order to conduct a successful DoS attack, malicious users often infect a number of computers with this type of Trojan in advance (for example, as part of a mass spam mailing.) As a result, all the infected computers will attack the victim machine.