is enabled in the browser, it downloads ga.js only once at the start of the visit. Furthermore, as all websites that implement Google Analytics with the ga.js code use the same master file from Google, a browser that has previously visited any other website running Google Analytics will already have the file cached on their machine. In addition to transmitting information to a Google server, the tracking code sets a first party cookie (If cookies are enabled in the browser) on each visitor's computer. This cookie stores anonymous information called the ClientId. Before the launch of Universal Analytics, there were several cookies storing information such as whether the visitor had been to the site before (new or returning visitor), the timestamp of the current visit, and the referrer site or campaign that directed the visitor to the page (e.g., search engine, keywords, banner, or email). If the visitor arrived at the site by clicking on a link tagged with UTM parameters (Urchin Tracking Module) such as: https://www.example.com/page?utm_content=buffercf3b2&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer then the tag values are passed to the database too. Limitations In addition, Google Analytics for Mobile Package allows Google Analytics to be applied to mobile websites. The Mobile Package contains server-side tracking codes that use PHP, JavaServer Pages, ASP.NET, or Perl for its server-side language. However, many ad filtering programs and extensions such as Firefox's Enhanced Tracking Protection, the browser extension NoScript and the mobile phone app Disconnect Mobile can block the Google Analytics Tracking Code. This prevents some traffic and users from being tracked and leads to holes in the collected data. Also, privacy networks like Tor will mask the user's actual location and present inaccurate geographical data. A small fraction of users don't have JavaScript-enabled/capable browsers or turn this feature off. These limitations, mainly ad filtering programs, can allow a significant number—sometimes the majority—of visitors to avoid the tracker. One potential impact on data accuracy comes from users deleting or blocking Google Analytics cookies. Without cookies being set, Google Analytics cannot collect data. Any individual web user can block or delete cookies resulting in the data loss of those visits for Google Analytics users. Website owners can encourage users not to disable cookies by, for example, making visitors more comfortable using the site through posting a privacy policy. As a user navigates between web pages, Google Analytics provides website owners JavaScript tags (libraries) to record information about the page a