What are the main types of PC viruses?
In general, there are two major classes of viruses. The first class consists of the FILE INFECTORS which attach themselves to ordinary program files. These usually infect arbitrary COM and/or EXE programs, though some can infect any program for which execution or interpretation is requested, such as SYS, OVL, OBJ, PRG, MNU and BAT files. There is also at least one PC virus that “infects” source code files by inserting code into C language source files that replicates the virus’s function in any executable that is produced from the infected source code files. File infectors can be either DIRECT-ACTION or RESIDENT. A direct-action virus selects one or more programs to infect each time a program infected by it are executed. A resident virus installs itself somewhere in memory (RAM) the first time an infected program is executed, and thereafter infects other programs when they are executed (as in the case of the Jerusalem virus) or when other conditions are fulfilled. Direct-action viruses
Generally, there are two main classes of viruses. The first class consists of the FILE INFECTORS which attach themselves to ordinary program files. These usually infect arbitrary COM and/or EXE programs, though some can infect any program for which execution or interpretation is requested, such as SYS, OVL, OBJ, PRG, MNU and BAT files. There is also at least one PC virus that “infects” source code files by inserting code into C language source files that replicates the virus’s function in any executable that is produced from the infected source code files (see E5 for a more detailed discussion of the issue of “executable” code). File infectors can be either DIRECT-ACTION or RESIDENT. A direct-action virus selects one or more programs to infect each time a program infected by it is executed. A resident virus installs itself somewhere in memory (RAM) the first time an infected program is executed, and thereafter infects other programs when *they* are executed (as in the case of the Jerus
