With the thousands of different browsers available today and with new browsers being added every day, you cannot cover all the different browsers and cannot hope to keep up with new versions that add the support that allows the new version of a browser to now run your script. To make things even worse, the field the only field that supplied an identification for the browser is the user-agent field which as its name implies can be set by the user of the browser. In fact most popular browsers make it easy to change the user-agent by supplying a built in switcher that allows the user of the browser to select from a list of several different browsers that they want it to identify itself as. Several of the most popular browser even allow adding user-agents to the list they choose from or even allow the field to be set to anything at all.
The script tests for the values that appear in the standard user-agent strings for the five most popular browsers as well as the two most popular mobile device identifiers and reports on which of those browsers and devices are unable to set the user-agent to contain the values it actually does contain.
This article written by Stephen Chapman, Felgall Pty Ltd.