Thanks for the heads up, but here's the only possible ways someone can hack your computer.

They would need to do one of the following:

1. Trick you to visit a website that installs something on your computer (possibly a trojan downloader that downloads the full virus) or that is a phishing website which steals passwords by providing you with a fake login page.

2. Physically be in front of your computer and install what they want.

3. Exploit a vulnerability in your OS (Remote desktop, shared root drives) - This is some serious shit if they can. However, they'd need your IP to even think about this. Even then, its very difficult and if someone could do this then they wouldn't waste their time stealing steam games or private information.
__________________________________________________ _____________________________

They can't just add you to friends and a virus installs. I wish it was possible, but it isn't. I'm not saying you should talk to them. By all means stay away from them. Its just 90% of viruses installed happen by victim interaction. If these guys aren't in front of your computer with things to be installed, they need you to do something. Yes, I did say it was possible for them to exploit certain vulnerabilities in an operating system, but assuming you have had no interaction with them and they are not part of 1% of hackers that just like to watch things burn, it is highly unlikely they'll be lucky enough to find an IP address. Looks like these guys just want steam accounts and games, if they just wanted things to crash and burn they'd do something a little more effective.

For anyone that says "But there are 1% that like to watch things burn" Imagine this. There are 100 snipers in the world that randomly shoot people. There are 6.8 billion people on the planet. The odds of you getting shot just walking around are about the same as you getting randomly hacked by someone you don't even know, have never talked to before, and have never seen.

So I wouldn't worry too much. This was post was just meant to explain to some people how shit works, if they are incredibly worried about this.

If I didn't explain anything in enough detail, or I missed something, lemme know.