Having a friend working as a network administrator at a high school, I can tell you that most of these network admins are overworked with nitty gritty paperwork and simply will not have the time to actively play the cat and mouse game with proxy websites. Only a very few minority will actually subscribe to our proxy newsletters from yahoo and google groups, search in yahoo answers, track the proxy listings for new free web proxies to be blacklisted and added to their school content blocks. Most netwok admins will completely rely on the school paid for content filtering systems such as websense, bluecoat, etc. Yes, there are some cases of them signing up in our proxy mailing lists every now and then. How do I know its them? Some used their work email accounts to sign up, without bothering for any stealth which once again highlighted their lack of time and dedication to fighting against bypass proxies. Some actually joined and then email us, the owners of the proxy newsletters to lecture us on the dangers of enabling school students uncensored internet access and to demand that we stop the proxy newsletter and our proxy business immediately. My proxy partner also told me about reading on a network admin's blog where he share self written scripts to analyze Internet access log files in his school and search for potential proxy sites that bypass school filters. Seriously, I do applaud their efforts and as long as there are internet filters, we will have business for providing web bypass services.
Many people are using free proxy sites to anonymously browse the net without leaving traces at the destination websites as well as at their network filters. They have learned that all the sites they visit during school and office hours are either being logged at the office firewalls or are already being blocked from direct access. Further persistent attempts to visit these blocked websites directly are going to raise a flag and they may risk losing their jobs for such unauthorized web surfing activities. At the same time, they are going to get some serious attention and questioning by the IT department if their work computers keep getting infected with the latest computer virus and spyware. We all know where such malware can be frequently found - definitely not on legitimate sites such as wikipedia and yahoo. Once you get the IT department on your trail, they can dig out your entire internet surfing history, mostly filled with exotic pictures and exciting videos totally unrelated to your work scope. Rather than risk their computers or jobs for viewing some blocked sites while being bored at work, they have learnt to use free anonymous web proxy sites to surf anonymously without exposing their real web destinations to the office internet content filters and to bypass blocked sites. Some people are still worried as to whether using proxy websites for unblocking websites are really legal or not. Basically, there is really nothing illegal about using a proxy server for surfing websites legitimately. It is an acceptable method for protecting your computer from hackers, computer viruses, spyware etc that are common on the web. If what you are doing online without using a proxy website is legal, doing so via a proxy does not change it legally. If you are only trying to unblock and hide your access to facebook during the lunch hour, you do not have to worry about infringing the law. However, infringement of company policies are a different issue. The only thing that matters is whether you are caught or not. As a whole, using anonymous web proxies is legal but proxies are also frequently used by shady people to conduct illegal online activities because proxies can help to hide their tracks and IP identities. It is this context where anonymous proxies can appear to be a gray subject - they are legal but can be easily used for illegal activities, it really depend on what your intent is about. However, if you think that you can abuse the free open proxy for blatant illegal activities, you will most likely be caught up and subjected to criminal proceedings based on what you have done through the proxy server.
It is perfectly legal to manage free proxy websites nowadays, at least in the US. Although you may be contacted by law enforcement to assist their investigations, all you need to do is comply politely with their requests and you will be fine. These officers know the nature and purposes of proxy websites so they know that any questionable internet activities are probably attributable to the vast number of proxy users and not directly due to the proxy webmasters. Just give them your server logs to help them track down the person they are after.