The author of this site tracked the performance of any stocks that he was offered in a spam email for a few months. His results were unsurprisingly horrible. In his words,
"almost ALL of those stocks I added went up a few cents max, then dropped like flies the next day."What do those results tell you about why someone might send a spam email advertising stock that they own? How might those spammers make money off the stock if they only increase a few cents the first day and then drop sharply?
(Source: Marginal Revolution)