Small
browser windows that pop up when you visit a
web page.
Geocities is
notorious for this (
but...), but it's common -
Real, et al, does it. There are
infinite pop-up porn ads, done also by some
MP3 and
warez sites - these are worse, since a browser (well,
Linux Netscape 4.x) is more likely to
crash under the strain of opening a bunch of pages from the livehotsex.com domain.
I was only clicking an unrelated AltaVista search result, honest.