Interesting. I wonder if anyone has built (or it would make any practical sense) a distributed silent bot net not for DDoS of websites but rather of math.

Imagine a small, otherwise-benign virus which simply spends some of your CPU cycles cracking something. Computers are pretty fast these days. It'd sure be easier to brute-force attack a password with thousands of average computers than one big one.

(I realize it'd probably be vastly easier and more practical to simply buy cloud-based CPU cycles, of course.)