Types of Malicious Codes

Malware

Malware, short for malicious software, is a kind of software that can be installed on a computer without approval from the computer's owner. There are different kinds of malware that can hurt computers, such as viruses and spyware. These programs can steal passwords, delete files, collect personal information, or even stop a computer from working at all. Before the term malware was coined by Yisrael Radai in 1990, malicious software was referred to as computer viruses. The first category of malware propagation concerns parasitic software fragments that attach themselves to some existing executable content. The fragment may be machine code that infects some existing application, utility, or system program, or even the code used to boot a computer system.

Types of malicious codes

Viruses are a kind of malware that need a user-run program to work. They cannot copy themselves or move from one computer to another without a program to host it. Viruses are very common in pirated programs. They can harm computers in many different ways, like deleting files and stealing passwords.

Worms are a lot like viruses and can cause the same kinds of damage. However, they're able to move through the internet and copy themselves onto computers without help from a host program. This makes them more dangerous than a virus. Worms are usually found in emails and drive-by downloads.

Trojan horses are like a much more dangerous version of a virus. They need a user to agree to run a program to work and cannot copy themselves from one computer to another. However, trojan horses can make the same problems a normal virus can make. They can also allow the malware writer to control the victim's computer, install more malware, steal bank data, and more. For example, ransomware is a type of trojan horse that stops a victim from using their files until they pay the person who wrote the malware. Experts think that trojan horses are the most common type of malware in existence.

Adware is a type of malware that earns the program authors money with advertising. These programs show users ads and force them to use websites that make money for the malware writers. Adware will also find personal information about the victim (such as their age, race, and job). This is so the malware authors can sell the information to other people. A user can usually uninstall adware easier than most malware. However, this is still difficult to do without a specially-designed program.

Spyware is a more dangerous kind of adware that steals more information from a user. Spyware can steal someone's Internet traffic, account passwords, and anything they have typed into their computers. Spyware is also much harder to uninstall than adware is.

Rootkits can prevent a malicious process from being visible in the system's list of processes, or keep its files from being read. Once a malicious program is installed on a system, it is essential that it stays concealed, to avoid detection. Software packages known as rootkits allow this concealment, by modifying the host's operating system so that the malware is hidden from the user. Some malicious programs contain routines to defend against removal, not merely to hide themselves. An early example of this behavior is recorded in the Jargon File tale of a pair of programs infesting a Xerox CP-V time sharing system:

Backdoor is a method of bypassing normal authentication procedures, usually over a connection to a network such as the Internet. Once a system has been compromised, one or more backdoors may be installed in order to allow access in the future, invisibly to the user. The idea has often been suggested that computer manufacturers preinstall backdoors on their systems to provide technical support for customers, but this has never been reliably verified. It was reported in 2014 that US government agencies had been diverting computers purchased by those considered "targets" to secret workshops where software or hardware permitting remote access by the agency was installed, considered to be among the most productive operations to obtain access to networks around the world. Backdoors may be installed by Trojan horses, worms, implants, or other methods.