Trojans are often used to enable even more serious attacks. By hiding programs to be run later, hackers might gain access to other networks, or run DDoS attacks . The simplest Trojan horse replaces the messages shown when a login is requested. Users think they are logging into the system, so they provide their usernames and passwords to a program that records the information for use by the hacker. The most famous Trojan horse to date is probably Back Orifice, which was developed by the hacker group known as Cult of the Dead Cow.
Web pages are simply computer files stored in directories on a server computer.
If a hacker gains access to these files, he or she can replace or alter them in any way. The Republican National Committee, the CIA, and The New York Times are just three of the highly publicized web page defacements over the past few years. Many more are cataloged in the mirrored archives of Attrition.org . However, it replicated itself so efficiently and took up so much memory and computing resources on the internet that many computers crashed, and system administrators across the country were forced to take their machines off the internet. Modern-day virus writers often have malicious intent, however, and they use viruses and worms to spread destructive programs among unwitting hosts.