Viruses, Worms and Other Active Attacks
Active attacks, such as viruses and trojans, are techniques where a hacker manipulates or deletes data to create the desired result.
Computer viruses were first seen in the late 1980s just as home computers were growing more popular. As its name suggests, a virus is a piece of code attached to a seemingly innocuous program and passed between computers. Once inside a system, the virus spreads and can bring down a computer.
Like a virus, a Trojan horse is simply a computer program. As the name implies, a Trojan horse fools the user into thinking it's another kind of program, and once installed, releases a malicious code.
Another cousin of the virus is the computer worm. Worms burrow into network security holes to pass and install malicious code from user to user. One of the most severe cyber-attacks of all time was through the accidental use of a worm by a graduate student in 1988, who was looking to determine the size of the Internet.
Software used for a variety of functions from disrupting a system to gaining access to a network is often called malware. Spyware serves to collect information on users and may or may not be malicious. Not all spyware is malware and vice versa.
There are also more niche subcategories of malware, such as ransomware, a term used for an attack meant to scare the user into paying what is essentially a form of blackmail, or scareware, a product falsely sold under the premise that it will protect your computer from outside threats.