Actually it's not phishing. Originally anyway.
What it is, is a trojan horse, I suspect one of the MyDoom, Bagle, or Netsky varieties, but once the trojan horse is installed on a Windows based computer, it then becomes a zombie machine.
With the trojan horse installed, anything could theoretically happen, as the author deems what he wishes to do with his army of zombie machines.
IIRC, Netsky had a few varieties that utilized this tactic, though they were often spoofed as being from administrator, management and a few others at the domain it was sent to.
Annoying at best, these things make a lot of people's lives horrible.
I still remember Macnutt.