TSR viruses are DOS viruses that remain resident in main memory after execution and from there infect all other executable files that are started after the virus. TSR is a term from DOS and stands for Terminate and Stay Resident (English for "Quit and stay resident").
As a rule, COM and EXE files are primarily infected by the virus, but device drivers and OVL files can also be affected.
In order for the virus to spread, an infected program must be running. This makes the virus memory-resident and usually infects every program executed after it, if it has not already done so.
TSR viruses can by themselves, for. B. intercept process calls, manipulate external storage media and cause even more significant damage to the system without the user having initiated any action.
Under ideal conditions, a TSR virus could even survive hard drive formatting .
TSR viruses can about the various BIOS - interrupts to access hard drive procure and check all write attempts to determine whether the own storage area in the master boot record to be overwritten. You prevent this or write your own MBR back after overwriting.
- Green Caterpillar. 1989