All of the modern firewalls filters like Websense can detect a proxy as soon as you connect to it. It’s actually incredibly trivial to do. The filtering software just tries to connect to the address in question. If it gets a response it’s a proxy and it’s then blocked. The only question is whether the system is set to auto block or if it emails or texts the admin and lets him do it manually, which can buy a few hours.
What needs to be considered is that in using a proxy to unblock school and work networks you are breaking numerous laws. Hacking a government (most schools are government run) security system is not legal. At work, you are probably also breaking laws about hacking as well as violating your employment agreement. Getting fired or suspended from school is a definite possibility at the least.
Even if you do get a proxy to work for a bit what do you get? A lot of these are hacker pots designed to either steal your information or plant bots on your computer that they can use. They use them to hide their identity by working through your computer and its internet connection. The recent Facebook and Twitter DDOS attacks that took down their entire networks is a classic example of what people using proxies and getting infected enables.
Even if it’s not a hacker pot it’s probably loaded with advertisements as that’s how the owner is making money. In either case the owner has no incentive to provide fast response or high bandwidth. The owner of the proxy is using you and delivering very little back to you. In fact, there is a good chance they are data mining you so they can sell your information to advertisers who want to target their ads. In most cases advanced web site features won’t work and only basic access will be available anyway.
At the end of the day you’re just wasting a lot of time that could be spent doing something more productive at best and risking your computer and more at the worst.
Read more about anonymous and free proxy servers below.
http://www.personalvpn.org/danger_proxy_servers.htm