Spam
Unsolicited e-mail/messages
Links
Links are a weak spot for some people. Links are a form of spam and if you click on one of those links then they can access a lot of information about you.
How to avoid it? Don't click on the links! It's as easy as that
Replying to Spam
Never reply to a spam e-mail. They just send out e-mails to a bunch of random addresses and see who replies. If you reply to one of those spams, then they have your e-mail and will keep sending spam to that address.
How to avoid it? Like I said, don't reply!