Worms, Trojans, and Keyloggers
Worms are similar to viruses, in that they are computer programs that can replicate themselves, and often contain some functionality that will interfere with the normal use of a computer program. However, worms are themselves separate programs and do not attach to other files or programs.
A Trojan Horse is another separate, malicious program, that will appear as something useful and needed, but is in reality quite harmful. A Trojan Horse enters your computer system through emails, external storage devices, or being downloaded directly from the Internet, but does not replicate itself. However, it can find your email account’s username and password and mail off more of itself to anyone in your contacts, so it can replicate in this manner. And then there is the rootkit, a malicious program or collection of programs so bad that once infected, your computer’s entire hard drive may have to be wiped clean and the operating system (OS) reinstalled. This is because rootkits are designed to compromise the OS itself and make it very difficult to remove once in your computer’s system.