This page is part of the WikiProject on open proxies, and is intended to be a source of information for users who find themselves blocked as open proxies.
Open proxy explanation
Every computer connected to the Internet has a unique numerical IP address assigned to it. Computers can also indirectly connect to the Internet through other computers; a computer network that allows computers to connect through it is called a proxy server. Such proxy servers can be highly useful, but are usually protected so that only authorized users can make use of them. An open proxy, however, is a proxy that anyone can use freely, by design or due to security vulnerabilities. Such security holes are often present without the knowledge of the owner, as in the case with many badly-configured ISP servers.
Because every computer is assigned a unique IP address, an effective method to stop a user who is abusing their editing privileges on Wikipedia is to block that address from editing. A problem arises with vandals who can change their IP address at will. Open proxies allow this, since connecting through them allows users to edit using that address instead of their own; blocks against that new address can be circumvented by switching to another address, and so forth. Automated scripts capable of doing this are especially disruptive.
For this reason, open proxies may be blocked from editing Wikimedia projects for any length of time.
Fixing the problem
Note: Many Internet service providers rotate customers through IP addresses, so it's entirely possible that you've been temporarily rotated to a blocked proxy. In that case, you should be able to edit again within a few hours or after reconnecting.
If you would like to edit Wikipedia, you can contact your Internet service provider to notify them that their proxy is open. Open proxies will be unblocked as soon as they are found to be closed. Due to the huge number of open proxies, these messages are not regularly sent out.
You may also want to ensure that your computer has not been compromised by malware which has turned your computer into an open proxy without your knowledge. Looking up your IP address on a "DNS Blacklist" such as the Exploits Block List at Spamhaus may be able to tell you what your computer or network has been compromised by.
Editing despite the fact
If you are knowingly using an open proxy to protect your identity, please note that your IP address is hidden when you register a username, and only a select few administrators and developers can check your IP address. Registering an account protects your identity without compromising your ability to edit Wikipedia.
If you are using an open proxy to circumvent a firewall, such as the national Chinese censor, please see Wikipedia:Advice to Tor users in China for a possible solution.
If you suspect that you aren't editing from a blocked proxy, you can request that the IP be rechecked by posting it under "Alerts" at the MetaProject on open proxies.