Almost all the zombie-computers (viral/trojan laden computers that are used by spammers worldwide to proliferate their crud) that display an IPA who are used by spammers are either: public proxies or connected to an educational network of various types.
Most educational networks have lax security -- surprising, but true -- compared with private enterprise (still also guilty but not as pervasively...hotels and public trading pc terminals are also among the worst zombie-affecting).
Many of the educational nets in places like Taiwan and China and Southeast Asia, Britain, etc., are all identifiable as having spammer-zombies.
So, actually, anticipating public-use pcs (that includes educational nets) to be more secure is foolish, given the higher degree of personal unaccountability that affects many terminals.
Educational networks are definitely a vulnerable point, but it was reported a week or two ago that AOL is actually the home of the zombie PC as far as malware generated from individual ISPs goes.
Whoda thunk.