Valve needs to grow a bit of a spine here.

The Call of Duty series is one of the worst offenders, effectively every game outside of the last 2 years has so many bad CVEs' and remote code exploits that even opening them on your PC is unsafe. Playing the official matchmaking on even something as recent as Black Ops 3 will have your computer compromised in minutes.

Yet they are still on the store front, they never go on sale. Black Ops 2 has been out for well over a decade and still wants full price for it on Steam & its unsafe.

Playing Call of Duty games on PC is probably the most unsafe thing you can do with your computer, outside of downloading malware itself.

Valve should delist these games from the store if they are effectively unplayable. They should ban Activision from selling new games on the store if they cannot make older titles even remotely safe. It's pure neglect, most of this stuff is fixed by the community with a few lines of code.

I'm not necessarily doubting what you say, however please could you provide us with a citation? The allegations you make appear quite serious.