Scammers have come up with a novel way to try and get around Steam Guard to steal your account. When logging in on a PC you havent used before, Steam Guard will pop a window asking for a verification code which will have been sent to your email address. Without the code, youll need to. grant access to this browser by uploading the special ssfn* file from your Steam folder. The SSFN file stops you from having to verify your identity through Steam Guard every time you login to Steam on your PC.”]
Source: https://blog.malwarebytes.com/cybercrime/2014/04/phishers-bypass-steam-guard-protection/