Virus Definitions

Virus
Computer virus is an application that replicates copies of itself and further spreads itself to other machines. Viruses do not have to be created by the experts, in fact most viruses can be (and were) written by average programmers.

Worm
These programs spread in a computer network and, like viruses-"companions", don't change files or sectors on disks. Computer Worms are viruses that reside in the active memory of a computer and duplicate themselves. They may send copies of themselves to other computers, such as through email , Internet Relay Chat (IRC), Peer-2-Peer Clients e.t.c.

Trojan Horse
A Trojan Horse or Backdoor open your PC from the inside to attackers. Once a trojan is installed, someone can take full control of your computer. Trojans are not viruses since they do not replicate, but Trojan horse programs can be just as destructive. Many people use the term to refer only to non-replicating malicious programs, thus making a distinction between Trojans and viruses.

Trojan-Downloder
The "Trojan-Downloader" programs contain information about the names and locations of malware programs to download and install. This information is usually stored as an encrypted block of data at the end of a "TrojanDropper" file.

Trojan-Spy or KeyLogger
Just as the name suggests if a program logs your every keystroke, it is considered a key logger. They are designed to steal your passwords and other sensitive information. There are two types of key loggers. One sends the logs to the author via email. Another one is stored in your hard drive. The author however would need the access to your computer in order to view the log. The second program can be installed on public computers, so beware and do not perform any sensitive procedures in public.

Porno-Dialer
Dialers are small programs which reconfigures your dial-up number to a premium rate number. If you use a dial-up modem to connect to your isp you are at risk.

Hoax
Hoaxes are simple gossips, designed to cause panic. The only thing they do is slow down servers, due to users informing their friends about a so-called "virus" by email, and waste people's time.

D.O.S. (DDoS)
D.O.S. stands for denial of service. These programs are designed to reduce the speed, cause outage of a service, artificially inflate bandwidth etc.