Scratch

There are a lot of evil people in the world today. Some are evil enough that they will take your stuff, even a domain name.

The domain scam I usually hear about is called Domain Name Slamming.
Domain slamming - what it is
Domain slamming is a process where people take your domain, and then charge you for it. What they do is they take your domain, transfer it to their services without your permission, and then charge you high prices for it. However, they sometimes send you fake domain expiration warnings asking you to renew it on their services.
Domain slamming - the usual signs
If you receive an email from someone that seems like your domain registrar warning you that your domain is about to expire or is offering an upgrade, and this email does not appear to be from the one you actually use or contains false information, then it is a scam email. Report it to your mail provider as fraud if possible, and maybe even report it to the Internet Crime Complaint Center.
Domain slamming - how to prevent it
-If you receive an email that fits the above description, do not follow its instructions. That is a sure way to get scammed.
-You should enable domain registrar locking to prevent this from happening, so it is near impossible to transfer the domain without your permission.
-Only do anything with your domain on the website of your registrar, and make sure you are actually on that website
-Take note of when your domains expire, so you know if expiration warnings are correct
-Renew your domains as soon as you can, because some people take domains as soon as they expire and sell them back at high prices
-And, just use common sense. Most of the scams are really badly executed and can be seen easily. You need the above steps for better thought ones.