Malicious code

Malicious code (sometimes referred to as 'malware') includes a variety of threats such as viruses, worms, Trojan horses, ransomware, and bots. Some malicious code is designed to take advantage of software vulnerabilities in a computer's operating system, web browser, applications, or other software components. Exploit kits are collections of exploits bundled together and rented or sold as commercial products.

A virus is a computer program that has the ability to replicate or make copies of itself and spread to other files. In addition to replication, most computer viruses deliver a 'payload' that may be benign or highly destructive, such as destroying files or reformatting the hard drive.

A worm is designed to spread from computer to computer and does not necessarily need to be activated by a user or program to replicate itself. The Slammer worm, for instance, infected more than 90% of vulnerable computers worldwide within 10 minutes. A Trojan horse appears benign but does something other than expected; it is not itself a virus because it does not replicate, but it often introduces other malicious code such as bots or rootkits.

Ransomware locks a computer or files and demands payment to unlock them; CryptoLocker, for example, encrypts files with virtually unbreakable asymmetric encryption and demands ransom in Bitcoins. Bots are covertly installed programs that respond to external commands from an attacker (the 'bot-herder'); the compromised computer becomes a 'zombie.' Botnets are collections of such computers used for sending spam, launching DDoS attacks, and stealing information.