I see that Graham Cluley has revised his excellent timeline article The short history of Mac malware: 1982 – 2011 on Sophos' Naked Security blogsite, bringing it up to 2011. (Thanks for the namecheck, Graham.)
As regards HyperCard viruses, I have seen it asserted that the first HyperCard infector was HC (also known as Two Tunes or Three Tunes, though nothing to do with the PC virus also called Three Tunes), which was reported in Holland and Belgium in 1991. However, as Graham observes, the message displayed by Dukakis clearly suggests that it was written in or before 1988. In fact, it's never been seen much, because it was intended to self-destruct...
The MerryXmas virus, sometimes claimed to be the "first documented" HyperCard virus, actually came even later.
1988 also saw the MacMag virus, which also spread via a HyperCard stack. However, the stack was a dropper, not viral in itself: it didn't infect other stacks.
I love a wallow in nostalgia. :)