The virus will normally infect an executable file and it will be executed when the infected file is executed. Some viruses only attack your system when the program that conceals them is run. Other, more sophisticated, viruses stay in your computer’s memory ready to attack anything that is run on the computer. These are resident, or memory-resident, viruses. A resident virus is one of the most common types of computer infections.
According to the mode of infection, the viruses are divided into resident and non-resident viruses. The non-resident virus has a module to find the files that it can infect. After infecting a particular file the virus will be executed when the infected file is executed.
In the case of the resident virus, the thing is different. They first infect a file or executed by some other means. When they are executed it loads its replication module into the memory. By working in the memory it is capable of infecting the files to a great extend.
Definition of Resident Virus
This is a type of malware that functions by installing malicious code into the memory of your computer. Depending on the virus’ programming, it can then infect any file run by the computer. This type of virus even attaches itself to anti-virus applications, thereby allowing it to infect any file scanned by the program. They are also known as the Terminate and Stay Resident (TSR)
They activate whenever the OS loads or operates a specific function.
A few examples of this kind of virus are Jerusalem Virus, One-half virus, Magistr, Junkie, Satanbug, etc.
Variants of Resident Virus
A resident virus has two types:
1.Fast infectors: Those which are capable of infecting a large number of files in a short duration. The fast infecting type virus is somewhat more dangerous since it infects more potential programs in a short duration. If the infected potential files include the files of the antivirus then there is a chance of infecting the files scanned by the antivirus. Fast infectors do massive damage quickly but are very easy to notice because of the effects.
The fast infecting virus shows the symptoms of infection very soon, mostly by slowing down the PC. There are antiviruses that will be active when there is an abnormality is identified and it will disinfect the infected file.
2.Slow infectors: In the case of slow infectors, they do not show the symptoms of infection as slowing down the PC. This makes them less chance to be identified by the antivirus. Slow infectors are able to spread more widely because they can go undetected for much longer. But do not remain unidentified forever. Since it shows the signs of infection very late, they are identified very late. However, it is less dangerous than that of the fast infectors.
Removal of Resident Virus
Removal of such viruses can be a bit tricky. Resident viruses need to be removed with an anti-malware software immediately, as the virus can potentially infect your entire anti-virus software.
A special virus removal tool that can extract the virus from the memory is required in most cases. It may be in the form of an OS patch or updates to existing virus removal software.