A computer virus is designed to infect files on a computer system through self-replication. It is capable of spreading to other computers on its own. Methods of infection include: infecting other files, email attachments, boot sectors of portable drives, instant messaging, and directly through security vulnerabilities in an Operating System or application. Not all computer viruses have a malicious payload, however, many do. Virus payloads are designed to do everything from deleting files on your computer to stealing your private information. Some are just made to disrupt operations on your computer or can be combined with other computer malware in a more complex package.
Methods of Computer Virus Infection
For a virus to spread, it has to execute its code and write to memory on a computer or computer periphery’s memory. Many viruses and other computer malware will attach themselves to legitimate applications or multimedia files in order to get the end-user to run them. There are two types of viruses that are classified based on the behavior observed after execution: resident and non-resident. A resident virus will not look for new hosts or other computers when executed. Instead, it will load itself into memory and then infect new hosts when the infected program is accessed. Non-resident viruses immediately search for new hosts to infect once they are executed.
Over the past few years, the latest trends in computer viruses have dealt primarily with polymorphic code. A polymorphic virus will infect files with an encrypted version of itself and then be decoded with an associated decryption set of coding instructions. The decryption module is also modified each time the virus spreads creating two unique pieces of programming code. This makes it more challenging for anti-virus programs to detect the virus. Some viruses go even further and exhibit metamorphic tendencies. This is when the virus completely re-writes its source code each time it infects a new program. Metamorphic behavior can delay the initial reporting of new computer viruses to the anti-virus companies until it exhibits classic behavior of computer virus infection to the end-user.
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