Trojan horse (computing)

Some computer programs act like tricks.

They look like helpful tools. But they hide bad things inside.

A trick program might look like a fun game. It might even look like a real email. If you click it, the trick starts. It can steal your secrets or bank info.

Some tricks can even take over your computer. They let a stranger watch what you do. This is why we must be careful.

To stay safe, do not click strange links. Always use good security tools. They help keep your computer healthy.

A trojan horse is a type of malware. Malware is bad software that harms computers.

A trojan hides its true goal. It pretends to be a normal program. It might look like a fun game or a real email. People often click on them by mistake. This can happen through fake ads or email files.

Once it is inside, a trojan can do many things. Some act as a backdoor. This lets a stranger access your device without permission. Others are called banking trojans. These try to steal money info, like credit card numbers. Some are called ransomware. They lock files and demand payment to fix them.

Some governments use special trojans. These are sometimes called govware. They can watch what people say on their devices.

You can stay safe by being careful. Do not click links from people you do not know. Use security software to find and stop them. Keeping your computer updated also helps. This fixes weak spots that trojans use to get in.

A trojan horse is a type of malware that hides its true intent. It works by pretending to be a helpful or normal program.

This trickiness allows it to bypass a user's defenses. Most trojans spread through social engineering. This means they use human tricks to work. A person might click a fake ad on the internet. They might also open an email attachment that looks like a routine form. Once the person runs the program, the trojan is inside the system. Unlike viruses or worms, trojans do not usually spread by infecting other files. They stay in one place to do their specific job.

Once installed, a trojan can perform many different tasks. Some act as a backdoor, which is a secret way into a device. This lets a controller gain unauthorized access to the system.

Many modern trojans contact Command and Control servers to wait for instructions. Other types are called banking trojans. These are designed to steal financial data like credit card numbers. Some act as downloaders to bring even more malware into the device. There are also remote access trojans, or RATs. A RAT gives an attacker full control over the computer. They can monitor what you do or even install more software.

The name comes from an ancient Greek story about the city of Troy. In that story, a deceptive wooden horse helped soldiers enter the city. The computing term has been around for a long time. By 1971, a Unix manual already used the term. A US Air Force report also mentioned it in 1974. Ken Thompson helped make the name very famous. He used it in a 1983 lecture about trusting software. He asked how much people should trust programs that claim to be safe. Because of this history, some people still capitalize the word "Trojan."

There are many famous examples of these programs in history. The AIDS trojan appeared in 1989 and was an early form of ransomware. Ransomware is malware that locks files and demands payment. In 2002, a famous program called "You Are An Idiot" appeared. It used a looping song and flashing faces to overwhelm computers.

Another major example is the Zeus trojan from 2007. Zeus targeted Windows systems to steal banking information. In 2016, the MEMZ trojan became known for making computers unusable. Some governments also use special software called govware. Examples include the Swiss MiniPanzer and the German R2D2.

Staying safe from trojans requires a few smart habits. You should always be careful with unknown files or links. Using security software like antivirus can help find and remove them. It is also important to keep your computer and apps updated. These updates fix security gaps that trojans like to use. In big offices, people use firewalls to block suspicious traffic.

You can also make regular backups of your important data. This helps if a trojan ever causes damage to your files. Being aware is the best way to stay protected online.

In computing, a trojan horse is a type of malware that misleads users. It disguises itself as a normal or legitimate program to hide its true intent. This deceptive nature allows it to bypass security defenses by tricking people into running it. Unlike computer viruses or worms, trojans generally do not try to infect other files. They also do not usually propagate themselves across a system on their own. Instead, they rely on social engineering to spread. This means they use human psychology to trick someone into executing an email attachment or clicking a fake internet advertisement.

Once a trojan is installed, it can perform many different malicious actions. Many modern versions act as a backdoor. A backdoor is a secret way for an attacker to gain unauthorized access to a device. These trojans often contact Command and Control (C2) servers over the internet. They wait there for instructions from a remote controller. Because individual trojans often use specific network ports to communicate, they can sometimes be detected. In some cases, other types of malware might even take over a trojan to use it as a proxy for further attacks.

Trojans are often classified by their primary function or their intended impact. Banking trojans are designed to steal financial information. They target online banking credentials, credit card numbers, or cryptocurrency wallet keys. Famous examples of this type include Zeus and TrickBot. Another category is the remote access trojan, or RAT. A RAT allows an attacker to gain full control over an infected system. They can monitor user activity or install more software. Some trojans act as downloaders, which means they serve as an initial infection stage. They install other malware, such as ransomware or spyware, once they are inside. Information-stealing trojans also exist to collect browser cookies and stored documents. Finally, fake antivirus trojans pretend to be security software to trick users into paying for harmful services.

The term is derived from the ancient Greek story of the deceptive Trojan Horse used to conquer Troy. While the exact origin of the computing term is unclear, it was in use by 1971. A Unix manual from that year assumed readers already knew the concept. Another early reference appeared in a 1974 US Air Force report regarding Multics computer systems. The term became widely popular due to Ken Thompson. In his 1983 Turing Award acceptance lecture, "Reflections on Trusting Trust," he discussed the difficulty of trusting software. Because the name comes from a legend, "Trojan" is often capitalized in older sources. However, many modern style guides suggest using a lowercase "trojan" for technical writing.

Some trojans are used by governments and are sometimes called govware. In German-speaking countries, this term refers to spyware used to intercept communications. Examples include the Swiss MiniPanzer and MegaPanzer, or the German "state trojan" nicknamed R2D2.

These tools often exploit security gaps that are unknown to the general public. They can access smartphone data before it is encrypted by other applications. This type of software is governed by legal frameworks in countries like Switzerland and Germany. The prevalence of trojans is a major concern for global security. A BitDefender survey from 2009 found that trojan-type malware accounted for 83% of all malware detected globally. Furthermore, about 15% of computers were estimated to be part of a botnet, which is often caused by trojan infections.

History shows many notable and sometimes strange examples of trojans. The AIDS trojan, developed in 1989, was one of the first forms of ransomware. It encrypted filenames and demanded payment to restore them. In 2002, the "You Are An Idiot" trojan became a famous example of a "pop-up bomb."

This browser-based trojan used a looping song and flashing faces to overwhelm users. It would spawn new windows every time a user tried to close one, eventually causing computers to freeze. The Zeus trojan, identified in 2007, was a major threat to Microsoft Windows users. It used man-in-the-browser attacks to steal banking data. In 2016, the MEMZ trojan became known for its destructive visual effects that rendered systems unusable.

Protecting against trojans requires a combination of technical tools and smart habits. Using updated antivirus and anti-malware software helps detect and remove infections. Maintaining regular updates for software and operating systems is also vital because it patches known vulnerabilities. In professional settings, organizations use firewalls and intrusion detection systems (IDS) to block suspicious traffic.

Modern security is also moving toward behavior-based detection. Instead of looking for known files, these systems monitor for suspicious patterns, like unauthorized privilege escalation. Machine learning is also being used to identify irregularities in large-scale network data to stop trojans before they can do damage.