The companies ARE legit, but they are being touted by these spammer scammers. The spammers flood the net with great "news" about company XYZ, people buy the stock, driving up the price, the spammers sell out, and everyone else is left holding the bag, because the value wasn't really that high.
As for WHY you're sending it out, it's because your box is being used as a mail relay. Even if you don't have a virus, you have ports open and the spammers know about it.
Yes - plus the stock tips arrive in the form of attachedimages so you can't even screen to elimate words in the text/body.
elimate = archaic form of eliminate, obliterate, erase...