CHROME RLZ

The RLZ information includes a non-unique promotional tag that contains information about how Chrome was obtained, the week when Chrome was installed, and the week when the first search was performed. This parameter does not uniquely identify your computer, nor is it used to target advertising. This information is used to understand the effectiveness of different distribution mechanisms, such as downloads directly from Google vs. other distribution channels. This cannot be disabled so long as your search provider is Google. If your default search provider is not Google, then searches performed using the address bar will go to your default search provider, and will not include this RLZ parameter. The RLZ means “Rules” project is a library for grouping promotion event signals and anonymous user cohorts. The tag looks similar to “1T4AAAA_enUS236US239”. This non-unique tag is included when performing searches via Google (the tag appears as a parameter beginning with "rlz=" when triggered from the Omnibox, or as an “x-rlz-string” HTTP header). We use this information to help us measure the searches and Chrome usage driven by a particular promotion.

Client applications with the RLZ library can use explicit cohort tagging to manage promotion analysis. A client application with a particular tag can transmit that tag as it chooses for payments and analysis purposes. As an example, the RLZ parameter "rlz=1T4AAAA_enUS236" indicates the client application is Toolbar version 4, distributed with AAAA software bundle, English version, to a US user. 

Installations of Google Chrome obtained via promotional campaigns also send a token when you first launch Chrome and when you first search from Google. The same token will be sent if Chrome is later reinstalled and is only sent at first launch and at first use of the Omnibox after reinstallation or reactivation. Rather than storing the token on the computer, it is generated when necessary by using built in system information that is scrambled in an irreversible manner. Google Chrome uses a software library called "RLZ" to generate and send this information.