Tor Browser Bundle leaks version info

https://svn.torproject.org/svn/check/trunk/cgi-bin/TorCheck.py it includes "There is a security update available for the Tor Browser Bundle." I saw that message live already.

How can check.torproject.org find out the Tor Browser Bundle version? This is not documented.

If check.torproject.org can do it, can other websites get the information as well?

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