Steam account - Query account by CD-key‏

No one is hacking your account, it just mean you ninja'ed a key and someone tried it.

It happens because the person tried to redeem a key you had taken. He got a message saying the key was duplicate, and clicked the link offering to claim the Steam account associated with the key. Don't worry, you can ignore it.

nothing to worry about

it happens when some1 tries to activate a key that you already activated (probably picked from forums or reddit etc) and clicks a button to email your account details to you

you probably ninja'd some key and activated a game, and eveyone else who's trying to activate that key gets an 'Duplicate Product Code' error with a nice button that says 'Retrieve account' that emails the owner of the steam account that used the said key.
There is nothing to worry about.

humble bundle send i message in that kind when you redeem a humble bundle gift link, (actually when it alredy redeemed you can ask to send a message to the e mail adress) or its some thing like thhat

I was to send a message to the steam forums, this post has saved me (i think)

people are calling everything hacking recently. :|

So you are able to find out account name by known cdkey? Or message with account name is just mailed to account with this key activated?

Thank you all for your replies!!!! I was quite worried, as I did not really have a clue as to what was going on. But now I know that I do not have to worry. Thank you, and many blessings to all of you who took the time to respond to my post.

Have a great evening all.

Thanks for this info ,had me wondering too.