Apple II Virus!??

[tursi@inasec.ca (Mike Brent)]

Hi, I just recently picked up a used Apple II computer, and have been 
reliving my younger days happily playing away. It's an Apple IIe with 
128k, and two floppy drives.
 
 One day, as I was working on a simple game, I saved my work. After several
 seconds, the cursor had still not returned... then I heard the drive head
 reset itself and begin to click across the disk. It sounded just like it was
 formatting. I was concerned, but waited. When the light went off, I did a
 CATALOG, and the disk was blank.
 
 I didn't know what to think... I figured something crashed.
 
 Later, I was playing around with Copy II plus and the disk sector 
editor, and I was reading the texts in the DOS tracks. Suddenly in the 
middle of the error messages I came across a bunch of garbage. I did a  
disassembly list, and found a piece of program code there.. it was self-
modifying code that incremented a counter and then branched to one 
address if it was ok, and to another if it wrapped back to 0. I also noticed 
at the end of the code it said 'BUGGER', and then continued with error
messages.
 
 Has anyone else run across this? Is it a virus? I didn't think the Apple II
 could have viruses?
 
Suggestions?