some thai try to hack my account with password verification code

[harry yoko]

i receive many mail written in thai from steam.apparently someone try toenter my accound and ask for a verificatin code.what to do.???..10 mails / day

[Jerry]

Changed your password already? That's pretty much all you can do. Your account name is permanent and hard-coded, so they got that one.
Scan for malware, if you haven't already. Also if you got the same login on any other website (not recommended, but it can happen), change it to something completely different there.

My usual standard tip for account safety as well here:
Don't enter Steam logins elsewhere. Instead, if a site asks you to log into Steam, go to Steam in your browser and log in there, then return. It should recognise you. If it still asks for your name and password then, it's not real.