An open proxy is a server that allows Internet users to connect through to hide their identity. The user sends their requests to the proxy instead of the destination server, and the proxy forwards those requests on to the destination. That destination server sends its replies back to the open proxy, which forwards them on to the user. There are many forms of open proxies, some intentionally set up as such and others being a side effect of security loop holes. Open proxies are often used to conduct questionable activities. Many sites, including Conservapedia and Wikipedia, restrict the use of open proxies due to abuse. Open proxies are often used by liberals who want to hide their location or ISP for unknown reasons. They are also sometimes used to circumvent local webfilters.
Open proxies often do not use encryption to secure the connection between them and their users, and some also declare the user's actual IP address to the destination server. They also have the ability to monitor and tamper with some of the data they handle. For these reasons as well as others, open proxies are not typically considered particularly secure. There have been multiple cases of open proxies were injecting foreign code into webpages which their users were viewing, although this has mostly been to get some money using advertisements.