INT 31 - VIRUS - "Vacsina" series - INSTALLATION CHECK (NOT A VECTOR!)
Note:	if one of the Vacsina viruses is resident, the low byte of this
	  interrupt still contains the last byte of the INT 30 CP/M(Control Program for Microcomputers) An early operating system for micros based on the 8-bit Intel 8080 CPU (and later the compatible 8085 and Zilog Z80 CPUs).  MSDOS version 1.0 was essentially a clone of CP/M for the Intel 8086. JMP
	  instruction, but the remaining three bytes are 7Fh 39h followed
	  by the Vacsina version number
SeeAlso: INT 21/AX=FFFFh"VIRUS",INT 32"VIRUS"