Spam bots are a type of macro seen in both free and members worlds. They, like many macros, have a randomised look and odd names, but they have also been seen in groups with nearly identical names aside from the numbers in it. These bots repeatedly say a predetermined phrase (or set of phrases in some instances) over and over, sometimes abnormally fast, and usually with multiple chat effects.
They will stand around in various banks (most commonly the Grand Exchange) or around Lumbridge advertising a website, usually an illegal real world item trading site, or a site containing a virus, and saying the same or similar messages over and over. Sometimes, gambling hosts use them to advertise flower games and other unoffical gambling games.
"Sell cheap GP 1m=$4.20 and items at illegalsite. Net!!~~~"