There are some fairly elaborate scams around to get your login information. I and each of my alts has been approached (by alts of the same person) on several occasions with the following cover stories:
"If you join my party, I'll give you items. I must log into your account to get you into my party."
"Download manabot from this web site: blahblah. (The web site prompted for my TMW login and password.)
"I found this great web site that will get you level 99. Log in and see for yourself." (web site wanted my TMW login and password, of course.)
"I know a cheat to get to level 99. I won't tell anyone, but I'll run it on your account if you let me log in."
lvledzero says he didn't give away his login info, and I believe him. Still, the grade of idiot who steals accounts in this game is far below the sort of person who can use malware to steal accounts. Frankly, those people have bigger things to attack.
I suspect the thief has been able to guess some passwords. There's a good summary of how to choose secure passwords at
https://isc.sans.edu/diary.html?storyid=1528
Briefly:
1) Don't use a word, a name, or all numbers. Base it on a sentence or lyrics to a song. "Mana World is fun, I play it every day!" becomes "MWif,Ipied!" (Yeah, guess that one baby!) (Do NOT use my example as your password!)
2) Write it down or store it in a secure program like Password Safe. Yes, I said write it down. Otherwise you'll end up choosing easy passwords, which is worse.
3) Use a different password for each site. If someone gets your TMW password, do you want them to log into your bank account? Your FaceBook account? Your Paypal account?
4) Don't tell anyone else your password. All reputable sites are designed specifically so that only you need your password, not them. If someone says they need your login info, they're up to no good. Just like in real life, you might trust some friends. If you do, it might be awkward if you discover things are missing from your account -- just like if your friend had a key to your home and your TV got stolen.
5) Changing your password every 30 days or whatever is not nearly as important as making it hard to guess (and hard for you to lose) in the first place. Most people change "g@rb@ge123" to "g@rb@ge456" anyway, which is useless.
Sources: SANS articles, Bruce Schneier's excellent Crypto-Gram, various vendor whitepapers and "best practices" documents, and my own experience in IT security.
You earn respect by how you live, not by what you demand.
-unknown