Every time you load TF2 or any other game and every time you disconnect from TF2 or any other game, you will be probbed on the port 27005 with that IP coming from the service HL2.exe(For Source only) It's checking your backpack, or cards, or game time, or way way more. Were there updates? Did you spend something? Did you get new items in your backpack? Steam does a LOT in the background, even when you're not playing video games.
If something malicious was trying to gain access to your PC that bad, they could overload your Commando firewall with specialized techniques and gain access. I don't think you're the target of anything malicious at this time.
Ports from 1024 to 49151 are registered ports, they are used by vendors. (Think Steam, Microsoft, Apple, etc) Any ports from 49151 and beyond are private/dynamic ports. That means that any program can run a service on the ports whenever it chooses.
If you REALLY wanna know what service is running on these ports, your firewall should be able to tell you.
p.s. Steam doesn't sneak around, make sure you read Steam's Terms of Service and if you sincerely think Steam is trying to breach your privacy, uninstall Steam and all Steam related products and never play on Steam again.