 This malware will react to disk I/O or execution events by infecting executable (.EXE or .COM) files when it is run and data files when they are opened.Parts of DOS itself, especially in DOS versions 5.0 and later, use this same technique to perform useful functions, such as the DOSKEY command-line editor and various other installable utilities which are installed by running them at the command line (manually, from AUTOEXEC.BAT or through codice_1 from within CONFIG.SYS) rather than loading them as device drivers through codice_2 statements in CONFIG.SYS.A TSR program can be loaded at any time; sometimes one is loaded immediately after the operating system's boot by being explicitly loaded in the AUTOEXEC.BAT batch program, or alternatively at the user's request (for example, Borland's Sidekick and Turbo Debugger, Quicken's QuickPay, or FunStuff Software's Personal Calendar).