[derefr]

Maybe not viruses much any more, but definitely worms. (And also some automated malicious servers scattered about the Internet that pull lists of devices with certain ports open from Shodan et al, and then repeatedly attempt to attack/penetrate whatever's on those lists.)

There are several videos available on YouTube, of someone connecting a Win9x/2K/XP machine to the modern Internet, waiting just a few minutes, and then observing (through Process Explorer) the silent introduction of various payloads onto the system.

[MikeRichardson]

Did those machines have public routable IPv4 addresses or something?

[uint8_t]

You didn't have a router with dialup, or early DSL, where the modem was a separate device. You'd often get publicly routable IPv4s in your university dorm, too. See also napster. :-)

[perching_aix]

Yes, they do.