Furthermore, information is sent to a relatively small group of people. As the name implies, a Trojan Horse program comes with a hidden surprise intended by the programmer but totally unexpected by the user. Trojan Horses are often designed to cause damage or do something malicious to a system, but are disguised as something useful. Unlike viruses, Trojan Horses don't make copies of themselves. Like viruses, they can cause significant damage to a computer.
Worms are like viruses in that they do replicate themselves.
However, instead of spreading from file to file, they spread from computer to computer, infecting an entire system. The rise in Internet use is paralleled by an increase in Internet-borne malicious code carried by Microsoft ActiveX controls and Sun Microsystems Java applets. Although it has not yet happened, it is possible for virus writers to use ActiveX and possibly Java to introduce viruses, worms and Trojan horses onto a web-surfer's computer, turning Web pages into virus carriers. By simply surfing the Web, users could expose their computer to viruses spread via ActiveX controls, without downloading files or even reading e-mail attachments. The virus writers could then use the virus to access RAM, corrupt files, and access files on computers attached via a LAN, among other things.