This is honestly a great moment for TF2 and the community itself. This will unleash so many possibilities and TF2 will continue to grow and develop for years to come. I am honestly very happy and grateful to Valve for making this decision and look forward to the times I will be spending on our servers.
Solution to hackers: $5 to create a Steam account.
...seriously though, people are totally overestimating the danger here - with the total amount of players going up we'll have an easier time filling up the servers, so the odds of having even one hacker at a time are ridiculous. Even if Valve DOESN'T come up with a good solution, worst case scenario you have to repeatedly kick someone until decent people join and fill up the server, and that would be incredibly rare.