Joan
it is very difficult to stop - in practice they are not as useful as the posters think as no links to other sites are possible and I trust none of the readers are silly enough to buy from them - they are generally removed when the administration clocks in in the morning (and the offending IP address is blocked), one approach is to force all contributers to recognise some random pictorial text but that makes it very difficult for those posters, like myself, who turn of graphics or use text based browsers for accessibility reasons - it is one of the many plagues of modern life, most emanating from the states (which is responsible for at least 60% of all spam, tho many reckon much more though in this case the hosting site is Australian) - it is merely a modern form of fly posting done by those who couldn't care less about the site they deface