Oldest PC virus?

The first time I had to wipe out a nest of pesky MBR virii it was the Stoned virus; the next one I encountered was Pakistani Brain, which Mikko Hypponen is claiming is actually the oldest virus, and then Jerusalem B (which was nightmarish compared to the first two).

Since we don’t know when Stoned was written, it seems a bit presumptive to assume that Brain came first. They were both encountered in the wild in the same year.