Are *.cer = *.crt certificates? Why auto-conversion when downloading from cacert.org?

[Guest Peter Stein]

When I try to download the root certificates (PEM format) from cacert.org

 

http://www.cacert.org/index.php?id=3

 

the IntExp 7 (under WinXP) automatically converts .crt (as visible in the status bar at the bottom of the browser)

to files with .cer extension.

 

Why?

 

Are there any differences between .cer and .crt certificates?

 

Frank