And If we started a thread for every Windows trojan..... 
A lot of which are based on the same code. The code is bought, tinkered with a little to change what the infected PC's display and repackaged. It's big business and Mac's are being targeted too.
Should I point out that Apple has also released more patches for their software than Microsoft, because it's more buggy and exploitable? It's just there were not enough users to make it profitable.
Also, I would like to point out this thread was started by an Apple user