Anonymous web browsing refers to utilization of the World Wide Web that hides a user's personally identifiable information from websites visited. Anonymous web browsing can be achieved via proxy servers, virtual private networks and other anonymity programs such as Tor. These programs work by sending information through a series of routers in order to hide the source and destination of information. However, there is never a guarantee of anonymity with these servers. These programs are still susceptible to traffic analysis. Proxy servers, which have a central point of knowledge, are also susceptible to collection of data by authorities. Moreover, cookies, browser plugins, and other information can be used to uniquely identify a user even if they have hidden their IP address.