An elaborate Steam scam is underway that pretends to be a free game giveaway site, but instead hacks a user’s Steam account, takes control over it, and then incorporates the new victim into their attack by targeting other players. The scam works by attackers hacking into Steam accounts and sending messages to the victim’s friends that they can get a free Steam game by going to a site and entering a promo code. If a user falls for the scam and enters their code, the site will perform a behind-the-scenes and automated attack that logins to their account, changes the password and changes the associated email address.
Source: https://www.bleepingcomputer.com/news/security/steam-accounts-being-stolen-through-elaborate-free-game-scam/