Spam *designed* to affect the economy, and not just for penis-enlarger purchases.
A spammer will purchase penny stock in a company, promote the company and encourage others to buy quickly, then sell off when the price peaks. This causes stock value to roller-coaster.
According to the Wikipedia, pump and dump scams became a major source of income for Organized Crime in the 90s.
While I was researching spam, I also came across this bit in the Wikipedia:
In early July 2006 there has been a massive increase in an unsolicited message from a spoofed address with a half dozen or so random letter subject which contains nothing but three lines of text from JRR Tolkein's The Hobbit. This follows fairly closely another similar form dubbed "discordian poetry" that appeared to used a random word generator dubbed "discordian poetry." In both of these there was no apparent attempt to sell anything and was theorized it was a skriptkiddie ineptly running a spamsuite, confirmed when shortly afterward the same format messages began appearing with image files overlaying the text (a common spam technique). It is suspected to be a variation from the same source and image overlays will begin appearing. []