A proxy server is a computer that offers a computer network service to allow clients to make indirect network connections to other network services. A client connects to the proxy server, then requests a connection, file, or other resource available on a different server. The proxy provides the resource either by connecting to the specified server or by serving it from a cache. In some cases, the proxy may alter the client's request or the server's response for various purposes. Web proxies
A common proxy application is a caching Web proxy. This provides a nearby cache of Web pages and files available on remote Web servers, allowing local network clients to access them more quickly or reliably.
When it receives a request for a Web resource (specified by a url), a caching proxy looks for the resulting url in its local cache. If found, it returns the document immediately. Otherwise it fetches it from the remote server, returns it to the requester and saves a copy in the cache. The cache usually uses an expiry algorithm to remove documents from the cache, according to their age, size, and access history. Two simple cache algorithms are Least Recently Used (Lru) and Least Frequently Used (lfu). Lru removes the least-recently used documents, and lfu removes the least-frequently used documents.
Web proxies can also filter the content of Web pages served. Some censorware applications — which attempt to block offensive Web content — are implemented as Web proxies. Other web proxies reformat web pages for a specific purpose or audience; for example, Skweezer reformats web pages for cell phones and PDAs. Network operators can also deploy proxies to intercept computer viruses and other hostile content served from remote Web pages.
A special case of web proxies are "cgi proxies." These are web sites which allow a user to access a site through them. They generally use php or cgi to implement the proxying functionality. cgi proxies are frequently used to gain access to web sites blocked by corporate or school proxies. Since they also hide the user's own IP address from the web sites they access through the proxy, they are sometimes also used to gain a degree of anonymity.
You may see references to four different types of proxy servers:
Transparent Proxy - This type of proxy server identifies itself as a proxy server and also makes the original IP address available through the http headers. These are generally used for their ability to cache websites and do not effectively provide any anonymity to those who use them. However, the use of a transparent proxy will get you around simple IP bans. They are transparent in the terms that your IP address is exposed, not transparent in the terms that you do not know that you are using it (your system is not specifically configured to use it.)
Anonymous Proxy - This type of proxy server indentifies itself as a proxy server, but does not make the original IP address available. This type of proxy server is detectable, but provides reasonal anonymity for most users.
Distorting Proxy - This type of proxy server identifies itself as a proxy server, but make an incorrect original IP address available through the http headers.
High Anonymity Proxy - This type of proxy server does not identify itself as a proxy server and does not make available the original IP address. Open Proxies, abuse, and detection
An open proxy is a proxy server which will accept client connections from any IP address and make connections to any Internet resource. Abuse of open proxies is currently implicated in a significant portion of e-mail spam delivery. Spammers frequently install open proxies on unwitting end users' Microsoft Windows computers by means of computer viruses designed for this purpose. Internet Relay Chat (Irc) abusers also frequently use open proxies to cloak their identities. Because proxies could be implicated in abuse, system administrators have developed a number of ways to refuse service to open proxies. Irc networks such as the Blitzed network automatically test client systems for known types of open proxy. Likewise, an email server may be configured to automatically test e-mail senders for open proxies, using software such as Michael Tokarev's proxycheck.
Groups of Irc and electronic mail operators run dnsbls publishing lists of the IP addresses of known open proxies, such as Blitzed opm and CBL.
The ethics of automatically testing clients for open proxies are controversial. Some experts, such as Vernon Schryver, consider such testing to be equivalent to an attacker portscanning the client host. Others consider the client to have solicited the scan by connecting to a server whose terms of service include testing. Anonymous proxy risksIn using a proxy server (for example, anonymizing http proxy), all data sent to the service being used (for example, http server in a website) must pass through the proxy server before being sent to the service, mostly in unencrypted form. It is therefore possible, and has been demonstrated, for a malicious proxy server to record everything sent to the proxy: including unencrypted logins and passwords. By chaining proxies which do not reveal data about the original requester, it is possible to obfuscate activities from the eyes of the user's destination. However, more traces will be left on the intermediate hops, which could be used or offered up to trace the user's activities. If the policies and administrators of these other proxies are unknown, the user may fall victim to a false sense of security just because those details are out of sight and mind.
The bottom line of this is to be wary when using proxy servers, and only use proxy servers of known integrity (e.g., the owner is known and trusted, has a clear privacy policy, etc.), and never use proxy servers of unknown integrity. If there is no choice but to use unknown proxy servers, do not pass any private information (unless it is properly encrypted) through the proxy.
Internet Anonymity
Internet anonymity is, in essence, the subject of internet privacy and its issues. Internet anonymity is basically the method by which people send messages and conduct business via the Internet without revealing their true identity. The information that they do reveal is controlled by the user him or herself. It includes the obvious personal information, however maintaining Internet anonymity extends far beyond the user: it includes computer information and location as well. To maintain Internet anonymity means to utilize the Internet without giving anyone the ability to trace or link web activity, or personal information, back to the user.
Those who are concerned about Internet anonymity often discuss several risks to personal privacy. Cookies are among the most talked about privacy risk. Cookies are text sent to a web browser about a site or page that has been visited. The text is stored by the computer’s server and sent back every time that particular web page is revisited. It makes for downloading the page quicker since the computer accessing the page is authenticated by the cookie. Cookies also contain specific information about the user, such as preferences, passwords, log-in IDs and even electronic shopping cart information. This is why the cookie is considered a privacy risk by Internet users, and has thus been disabled by many computer owners prior to surfing the web.
Advocates for Internet anonymity argue that it is the most important aspect of free speech on the Internet. Anonymity allows for Internet users to express themselves freely without worry of being discovered or tracked, ridiculed, or harassed. This is important to online discussions and forums, especially those involving personal questions or topics, in which those participating do not want to have to admit who or where they are. A perfect example of the importance of such anonymity is in medical forums where patients are free to ask medical questions of doctors or others with similar medical afflictions. Advocates also maintain that Internet anonymity is essential for transmitting information that must remain anonymous. The reporting of illegal activities and criminal behavior via the Internet is also an example of how vital anonymity can be: it gives witnesses and reporters the comfort and security necessary to offer their testimony.
Opponents argue that certain abuses and illegal activities are perpetuated by available Internet anonymity. Spam, or unsolicited email, is a common abuse of Internet anonymity. Most spam emails are junk mail and non-threatening; however, there have been cases where spam has been utilized to communicate hate-speech, threats, and harassment, and the anonymity of such spam has made it difficult, if even impossible, to track their originators. Opponents also debate that anonymity protects criminals and sexual predators. These offenders utilize the forums and discussions groups that protect the identity of all users to target their prey via the Internet.
The reality of Internet anonymity is that it will be a subject of heated discussion for years to come. Fortunately there exist avenues that Internet users can take to protect their identity, preferences, and IP addresses, if anonymity is important to them. Disabling cookies is common choice and some web browsers, like Mozilla Foxfire and Opera, have a setting that automatically deletes all cookies at the end of an Internet session. Overall, users need to remain cognizant of what information they provide on the Internet, including that in on-line screen names and profiles, if they want to maintain anonymity while using the web.