Maybe if you weren't so vague about in what manner you were to enforce this, it would be easier to help you. If you're trying to block your kid from playing. Theres a crappier but efficient option. Maybe it's someone who's 16. He's going to know how to use a computer. You're going to want to do something more advanced then. Changing port settings maybe. Maybe you're a teacher running a tech lab (under qualified then) but you could check to see the IPs for the login servers and use command lines to sever connectivity. If you're a smartie and you want someone to stop DLing that s*** on your computer. You could run your own code to deny access to certain websites. Flag Leagueoflegends.com in your browser and any other combination of what was previously stated.
Theres a reason why people take screen shots of their computer specs when figuring out computer options and stuff. Not that it applies to you, but the more information you give people the more likely they are to be able to or even want to help you.
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