Can someone enlighten me about how to use or implement the new feature - MAC cookie in hotspot's login page?

This link was in the changelog.

http://wiki.mikrotik.com/wiki/Manual:Ho ... MAC_Cookie

Maybe I'm missing something, but I cant find "MAC cookie feature " in ROS Ver V 5.25 (mibpsbe).
Is it available yet? reading the wiki it should be an option in hotspot user profile.
Anyone seen-using it?

It was added in RouterOS 6.

Is it feature realy insecure?
Somebody can take any already logged mac-address from the air and set it on the own wi-fi adapter.