HomeNews
Watch out: profile images on Steam could contain malwareBe wary downloading pics from Valve’s platform
Be wary downloading pics from Valve’s platform

World Premiere | Mystery Steam Reviews (Video Games Announced At E3)Watch on YouTube
World Premiere | Mystery Steam Reviews (Video Games Announced At E3)

Basically, you’d need to have downloaded some other bit of nasty malware (from rotten websites or spam emails) that would act as a decrypter. Damage can only be caused with both bits of malware.
“It should be noted that in order to become a target for this method, no installation of Steam - or any other game platform - is required. The Steam platform merely serves as a vehicle which hosts the malicious file,” G Data say.
If you’re interested in the technical bits, here’sthe link to that G Data articleagain where they explain in detail how the malware works.