Viral Rewind: Virus.DOS.Casino

Casino is an interesting DOS virus in that it literally puts the user's data on the line and makes them "gamble" for it with a slot-machine like game with five chances. When first accessed it will load into memory as a TSR hooking interrupt 21h to infect any .COM or .EXE programs as they're accessed. It's infections are somewhat stealthy as the infected file size doesn't change but available free space will show as decreased.
The Payload: Whenever the month is January, April or August and the day is the 15th it will activate when an infected program is run. It displays several lines telling the user their FAT (File Allocation Table) is corrupted and the good copy is stored in the computer's memory. If they win Casino will restore the FAT; if the user loses the game or restarts/powers off before the FAT is restored their data will become inaccessible/lost.
The user is given five chances (credits) to get three pound marks (£-£-£). If they do they win the "game" and their FAT is restored. The program then halts the computer warning the user to power off their system and not use it again till the following day (as the payload activation will be outside its date). Otherwise Casino may start again.
If the user uses all their chances or they get three question marks (?-?-?) the game ends and Casino does not restore the good FAT and hangs the system rendering any data on the disk inaccessible/lost.
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