Update May 2012-
I would have a bootable USB stick and run a pocket LINUX version today. Or if USB Boot is disabled in the BIOS then the Phone tether method also works with USB or wirelessly. Then you have no filters, blocks or issues. You can install anything and run it to access the network.
Now that everyone has phones with internet service is no big deal to get to your mail and webpage anymore.
It is cheaper to use WiFi calling or surfing than 3G or 4G services, so look for open or public WiFi and use your phone connected and preferenced to WiFi at home, work or mall etc.
Stuck at school? Setup your phone to VNC or RDC "remote" into your computer at home. Then just control from anywhere.
Grounded, cut off....awwww. Even game consoles can run LINUX. If you have anything with a CPU someone has unlocked it.
At school, in a library or mall and have access to a PC but cannot "surf" to any thing but their one site or a "filtered" subset of the internet?
Is Youtube blocked?
Is iTunes, Bittorrents or other sites blocked?
Can you not download or installed software?
Ok...we'll try to help you dorks out.
Step 1: Overview
They have to block ALL exploits and all access to command line, process startup/control and downloads...plus keyboards, admin roles, powerusers or even USB ports and BIOS firmware!
if ANY of these are exploitable then we have means to attempt to access any system's internet access....or a cooler idea is to enable a PC's "ICS" Internet Connection Sharing, or peer-to-peer wireless 802.3 even Bluetooth and use your Bluetooth or WiFi phone, pda or itouch to then surf 'unobstructed' ! hehe
I'll provide follow-up steps for EACH below as time permits.
1) Simple browser filter or cheap software like netnanny etc.
We exploit this with a proxy or web redirector and kill -f process name or id
2) Advanced Network filter and site blocking
Many proxy or redirector will bypass these as well, where they do not we also use advanced proxy services like the Vidalia bundle , TOR, Prioxy & Vidalia
3) Keyboard disabled or missing
OH soooooo easy, Microsoft allows for "disabled" users with an on-screen keyboard! duh
4) Kiosk Mode IE
OMG even easier! ALT+f4 logs off IE and then start whatever you want as above or see below....
5) Starting and stopping processes, killing or modifying msconfig etc
helpful for custom downloads or setup of exploits above
6) Basket / Corner cases
tough nut? Post your isseus
You need to research the environment, use human engineering develop specific exploits and then go get 'em...
Step 2: Cheap Filters or Software
Try to go to youtube or other "prohibited" sites and see what the message and source is of the "blocked" URL that is returned....what's the software? What's The message?
While we cannot address ALL the many permutations and software here, you can use Wikipedia and the vendors support pages for clues to get detail implementation information.
a) see if proxy or web redirectors are also blocked...try the url's below. Enter the prohibited site in the box on their webpage...<wink>
Google "free anonymizer" for more links
b) if it fails see if message differs for original, try a different anon site.
main pagemain page
proxy list 
proxy list 
proxy list 
proxy list 
proxy list 
If these ARE available then use them, be patient, the FREE sites are slow or busy the pay sites are often unreasonable but logins or access can also be hacked...that's ANOTHER instructable.
Step 3: Top Ten from the Home Office!
1. Use IP address - This is the simplest way to bypass domain name based access restrictions. Instead of the domain name such as www.webstuffscan.com use the direct IP address. To find the IP address use one of the free host to IP online conversion tools such as http://www.hcidata.co.uk/host2ip.htm
2. Use Google cache - If you are not bothered whether the content is latest on a site, Google cache is best. Do a Google search for the site and then click on the cached link below the search results.
3. Use an Anonymizer - In this method you access a third party site which in turn routes your request to the required server. Some services provide URL encryption also. The problem is that most of these servers are no longer free. Do a google search for the latest list as this is a very dynamic area Following are some services which still works(free!),
Daily Best Links - Hides original URL and provides an array of access of options. The is one of the best free servers.
Anonymouse - This works, but URL is visible and hence may be blocked by the filtering software.
4. Use Online Translation Tools - In this method, we can use the translation service as a web proxy. Following are the best links I know of. Again Google is your best friend for more resources.
Altavista Babel fish - In the above replace www.webstuffscan.com with the site you want. You can also visit Babel fish site.
Google Translate - Similar to Babel fish.
5. Use Google Mobile search - Google mobile search works, but output may not be optimal. This is very similar to using a Web proxy.
6. Use a public Proxy server - There are many free proxy servers out in the Web. Note that in order to use these you have to change internet connection settings in Internet Explorer or whatever browser you use. This is one such list. http://www.publicproxyservers.com/page1.html
7. Get web pages via email - This is useful if you need a single Web page. Obviously accessing large files is not possible. Given below are some examples.
You can use SEND http://www.yahoo.com/ in the body of the message and send it to firstname.lastname@example.org to retrieve yahoo.com home page.
You can also check out services at web2mail which includes web page subscriptions.
G.E Boyd has an extensive list of servers. Note that many in the list are no longer working.
9. Use Tor Distributed Proxy - Tor is an advanced proxy server using multiple anonymous servers for a single Web request. This requires an application to be downloaded and installed.
8. Your own proxy server - This is an advanced technique and is probably the best. This requires your own proxy server hosted either at your home or at a hosting service provider. You can enable SSL encryption and prevent any snooping on the content as well. Also put some access control, otherwise someone can find the service and misuse it (Trust me, there are many who are looking for such an opportunity!).
Use Apache Web server as proxy server - A bit complex setup.
Use Privoxy - - This is the recommended approach. Please see this page for more details.
Use PHPProxy as a Web Proxy - You can use PHPProxy to setup a Web proxy.
10. Use alternate content providers - When everything fails, you can use alternate service providers. For example if Gmail is blocked at your place, you can take another obscure mail address and enable email forward at Gmail.
Be careful when you are using public proxy servers. It is possible for the guy who is hosting the service to snoop on the data that is passing through. So I wouldnÃ¢â¬â¢t recommend putting any important information such credit card details when you are using public proxy server method.
update 1 (Nov 26) - Sharjeel has got an impressive list of 300+ web proxies.
update 2 (Dec 22) - Check out my latest how to on running your own windows Http proxy server.
update 3 (Feb 01) - Please see comments below for some good tips. Also some of the sites mentioned in the article are no longer working.
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