Help, quickly this is important, pc has been infected what to do

[TheAterix]

My friends steam account has been hacked and it was a file that someone had infected his pc with, when he joined a lobby it downloaded a file and then his account was gone, i think it is an infection that has been injected into his pc.
He is extremely worried as it could potentially take credit card details he has saved etc, if you can help me that would be absolutely amazing, and also, as fast as you can!]
Any help on what to do next is massively important!

 

[ss202sl]

Log into Steam on a different computer. Then remove any credit card information.

Then you can worry about cleaning the virus

 

[Adinathjuparkar]

don't keep the steam login on automatic login and change the email and password for further protection .................the virus makes your account available for the hacker and he can use your account for further spread of virus and even misuse it so next time dont download any file from chat