How to regain access to your account:
Contact Steam Support and a support agent will verify that you are the owner of the account and restore account access to you. You may be asked to provide proof of purchase for games on the account or proof of ownership of the payment method.
More information is available here: Reclaiming a Hijacked Steam Account FAQ, Account Security Recommendations
This account will have restricted functionality until the owner has regained access.
Purchasing, gifting, trading, cd-key activation, and Steam Community access have been disabled.