Trojan horse (computing) in the context of "Trojan Horse"

Malware (a portmanteau of malicious software) is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, deprive access to information, or which unknowingly interferes with the user's computer security and privacy. Researchers tend to classify malware into one or more sub-types (i.e. computer viruses, worms, Trojan horses, logic bombs, ransomware, spyware, adware, rogue software, wipers and keyloggers).

Malware poses serious problems to individuals and businesses on the Internet. According to Symantec's 2018 Internet Security Threat Report (ISTR), malware variants number has increased to 669,947,865 in 2017, which is twice as many malware variants as in 2016. Cybercrime, which includes malware attacks as well as other crimes committed by computer, was predicted to cost the world economy US$6 trillion in 2021, and is increasing at a rate of 15% per year. Since 2021, malware has been designed to target computer systems that run critical infrastructure such as the electricity distribution network.

Cyberweapons are commonly defined as malware agents employed for military, paramilitary, or intelligence objectives as part of a cyberattack. This includes computer viruses, trojans, spyware, and worms that can introduce malicious code into existing software, causing a computer to perform actions or processes unintended by its operator.

A logic bomb is a piece of code intentionally inserted into a software system that will set off a malicious function when specified conditions are met. For example, a programmer may hide a piece of code that starts deleting files (such as a salary database trigger), should they ever be terminated from the company.

Software that is inherently malicious, such as viruses and worms, often contain logic bombs that execute a certain payload at a pre-defined time or when some other condition is met. This technique can be used by a virus or worm to gain momentum and spread before being noticed. Some viruses attack their host systems on specific dates, such as Friday the 13th or April Fools' Day. Trojans and other computer viruses that activate on certain dates are often called "time bombs".

Ransomware is a type of malware that encrypts the victim's personal data until a ransom is paid. Difficult-to-trace digital currencies such as paysafecard or Bitcoin and other cryptocurrencies are commonly used for the ransoms, making tracing and prosecuting the perpetrators difficult. Sometimes the original files can be retrieved without paying the ransom due to implementation mistakes, leaked cryptographic keys or a complete lack of encryption in the ransomware.

Ransomware attacks are typically carried out using a Trojan disguised as a legitimate file that the user is tricked into downloading or opening when it arrives as an email attachment. However, one high-profile example, the WannaCry worm, traveled automatically between computers without user interaction.

Cyber espionage, cyber spying, or cyber-collection is the act or practice of obtaining secrets and information without the permission and knowledge of the holder of the information using methods on the Internet, networks or individual computers through the use of proxy servers, cracking techniques and malicious software including Trojan horses and spyware. Cyber espionage can be used to target various actors – individuals, competitors, rivals, groups, governments, and others – in order to obtain personal, economic, political or military advantages. It may wholly be perpetrated online from computer desks of professionals on bases in far away countries or may involve infiltration at home by computer trained conventional spies and moles or in other cases may be the criminal handiwork of amateur malicious hackers and software programmers.

Turla or Uroboros (Russian: Турла) is a trojan package that is suspected by computer security researchers and Western intelligence officers to be the product of a Russian government agency of the same name.

High infection rates of the virus were observed in Russia, Kazakhstan and Vietnam, followed by US and China, and low infection rates in Europe, South America and Asia (including India).