A lotta times, spambots "generate" email addys by "brute force" - randomly stringin' together characters and appending them to a known email domain such as hotmail or Yahoo or AOL or whatever. Not much you can do abput that, short of spam-blockin' software. Most premium email provoders now offer some sort of spam filtering; check your "Preferences" or "Settings" from your user profile page. Another frequent occurrence is that your email addy may have been harvested by a trojan or virus runnin' on somebbody else's machine which had your addy among those in that machine's address book. Once its out there, its out there.
Somethin' you may find of interest:
Stop Spam FAQ
Another good reource, with lotsa look-further-into-it links:
Coalition Against Unsolicited Commercial Email
A final observation - in most cases, usin' the "opt out/unsubscribe" link in a spam message does nothin' more than confirm to the sender they've hit a valid, workin' mailbox. Even if you get yourself removed from that particular advertiser's mailin' list, your addy goes on a "known active" list which is sold to others.