Scammer(https://steamcommunity.com/profiles/76561198378304894) send messages to victims for inviting to exchange in-game items. He let you to connect to legit trading website. (e.g. csmoney, bitskins) And also, he introduce fake website(https://suffinfo.com/) to check item's price.
fakewebsite do picture-in-picture attack. It steals victim's account ID and password and also 2FA code.
Login window is totally fake(with picture-in-picture attack, it seems totally legit)