Details on "User Agent Info"


I recently started testing and playing around with Piwik. I have been using Awstats for some time and wish to also implement Piwik to the reports.

My question is simple but complicated :S

Basically I would like to know:

  1. How does Piwik identify the users “user agent information”, is this a plugin or part of the core?
  2. How often does this “database” of “user agents and operating systems” gets updated ?
  3. Can add / Modified “user agents / operating systems” ?

Thanks in advance for any information you can provide.