Private Browsing

Today with private browsing you can indicate 2 different things:

1. Browser capability of going "stealth"
   
2. Private browsing with anonymous proxy and others mechanism
   

Browser option

"InPrivate Browsing" in Internet Explorer, "Incognito mode" in Chrome, and "Private Browsing" in Firefox and Safari all strive to do the same two things: make it impossible for users of the same computer to figure out which sites the browser has been used to visit, and make it impossible for sites to know whether or not a particular user has previously visited them.

To keep browsing private from other users of the same machine, browsers must discard (or avoid creating) any history entries, cached items, cookies, and so on. To prevent sites from being able to track visitors, the browsers must ensure that they don't send any cookies or other identifiable information from non-private sessions when in private mode.

So it's all so private ?

On Arstechnica site there are some result of Stanford University study on privacy made with the 4 more used browser. The test found that the browsers' protections were imperfect. Browsers did not properly isolate their private sessions from non-private ones, with the result that suitably crafted sites could trace visitors between private and non-private sessions. Sites could also leave persistent indications that they had been visited, allowing visits to be detected by local users.

The big problem: add-ons

The problem got worse when extensions and plugins were considered. All four browsers tested enabled plugins in private mode, and these plugins can themselves store data that allows both kinds of privacy to be defeated. 

One example of such a plugin used to be Adobe Flash; Flash has its own cookie system, and it used to be the case that Flash's cookies did not respect the privacy mode of the browser. Cookies set in private mode persisted, and cookies set in public mode were readable from private mode. Fortunately, Flash has since been fixed, but any plugin could contain similar errors.

Internet Explorer and Chrome both disable browser extensions by default in their private mode; Firefox, however, does not, and this provides yet another avenue by which private information can be leaked.

A degree of anonymity can be achieved by using a proxy server or a VPN server. If the proxy server is trusted, anonymity will be retained because only the information on the proxy server is visible to outsiders.

Anonymous web browsing is generally useful to internet users who want to ensure that their sessions can not be monitored. For instance, it is used to circumvent traffic monitoring by organizations which want to find out or control which web sites employees visit.

Anonymous Web Servers work by placing a wall between the user and the website that he/she is visiting. These servers can be used to bypass restrictions and visit sites that might be blocked in a specific country, office or school. Some people only use these servers to protect their online identity.

Of these services one i've used and found easy to install and use is TOR

Tor is a system intended to enable online anonymity, composed of client software and a network of servers which can mask information about users' locations and other factors which might identify them. Use of this system makes it more difficult to trace internet traffic to the user, including visits to Web sites, online posts, instant messages, and other communication forms.

It is intended to protect users personal freedom, privacy, and ability to conduct confidential business, by keeping their internet activities from being monitored.

The software is open-source and the network is free of charge to use. Though the name Tor originated as an acronym of The Onion Routing project, the current project no longer considers the name to be an acronym, and therefore does not use capital letters.

Tor is an implementation of onion routing, and works by relaying communications through a network of systems run by volunteers in various locations. Because the internet address of the sender and the recipient are not both readable at any step along the way (and in intermediate links in the chain, neither piece of information is readable), someone engaging in network traffic analysis and surveillance at any point along the line cannot directly identify which end system is communicating with which other.

Furthermore, the recipient knows only the address of the last intermediate machine, not the sender. By keeping some of the network entry points hidden, Tor is also able to evade many internet censorship systems, even ones specifically targeting Tor