If you have reverted your mac to Snow Leopard from Lion, its important that you also remove the Recovery HD, as it can compromise the security of your Snow Leopard installation (for security issues with Lion, see here). Reverting to SL via Time Machine or restoring from a clone will leave the Recovery partition in place, meaning anyone can boot into it and reset your Snow Leopard passwords merely by restarting your mac while holding down the ‘option’ key.
To remove the Recovery disk follow this procedure:
1. Revert back to Snow Leopard using Time Machine or a clone.
2. Once you’re up and running and have confirmed everything is good, go to Terminal (Applications > Utilities > Terminal) and paste/type this command to confirm the presence of the Recovery HD:
then press ‘Return’. If you see a partition labelled something like this
Apple_Boot Recovery HD (see image above)
then you will need to continue with the rest of the procedure. If the Recovery HD is not listed here, you do not have the Recovery partition and need not worry further.
3. If you find the Recovery HD in the list, paste the following command into Terminal:
defaults write com.apple.DiskUtility DUDebugMenuEnabled 1
Now open Disk Utility (Applications > Utilities > Disk Utility). In the menubar at the top, choose Debug > ‘Show every partition’
On the left in the main Disk Utility window, you’ll be able to see ‘Recovery HD’ (it’ll be greyed out). You can click ‘Mount’ in the taskbar to make it active, and you can now delete it using control-click/right click – erase or by using the ‘erase’ tab in DU’s window.
If you want to confirm that the Recovery disk is no longer present, go back to Terminal and type the command from step 2.
how to secure your mac (OS X Lion)