From a piece on botnets by Ed Felten I read today:
Estimates vary, but a reasonable guess is that between one and five percent of the computers on the net are infected with bots.
Man even 1% of the internet is a lot of computers and it's hard not to believe that they are 99.9% Windows. But his piece is full of amazing stuff, another part that I thought was priceless:
Nowadays, bots often fight over territory, killing other bots that have infected the same machine, or beefing up the machine's defenses against new bot infections. For example, Brian Krebs reports that some bots install legitimate antivirus programs to defend their turf.
Bots installing antivirus programs to protect themselves from other intruders?! Ed's piece is well worth a read.