Easiest ways I have learned from reading on how to steal live or ps3 accounts..
1. they get the gamer tag.. You know the ones in the OP
2. then they glean extra info that could be tied to the account, city, school, college, info that is usually posted in profiles, facebook, you can google the rest usually..
3. they call customer service and try to switch stuff over. Generally you will get asked info that most gamers have easy answers for.
4. then they hijack the account.
There is not really a lot you can do unless you don't show your gamertag and where you are from.. Maybe have this thread not be public and only to veteran members would be wise..