SPAMmers are very shady when it comes to collecting your e-mail addresses. They will look anywhere on the internet for an e-mail address to add to their list. Anywhere they can find an e-mail listed, most likely they will add it to their list. Spam is still a very effective way to get people to visit sites, or to advertise a certain something. Believe it or not, quite a number of people actually open e-mails that are so obviously spam. So set your e-mail filter settings to try and block most of it, and don't open anything that you aren't fairly sure is safe. Because, spyware and viruses are still sent through the e-mail.

How to prevent spam

Be very careful about what sites you send your address to. Most legit sites will explicitly state that they will not sell your address. If they don't state this, it's anybody's guess as to whether or not it'll end up on some SPAMmers list. Also, Don't click unsubscribe to any SPAM that you know isn't from a legit source, because doing so will just verify to them that your e-mail address is active. Try to have a separate e-mail account that you can use if you want to sign up for something from a less than respected website.