Sorry, but the user can always change it, very easly.
First of all, the things I said about manually editing the registry also applies to Messenger Plus! settings. All it takes is changing 1 registry key to disable chat logging:
HKEY_CURRENT_USER\Software\Patchou\Messenger Plus! Live\
<Windows Live Id>\Preferences\EnableChatLog
No matter if you have protected the options with a password or not.
Second, the password protection of preferences in Messenger Plus! is extremely weak and is only there for '
accidental changes'. Again, all it takes is deleting one registry key to have access again to the preferences via the UI of Messenger Plus! Live:
CookieRevised's reply to Preferences Password
Third, Messenger Plus! must be installed and running in order to log messages with Messenger Plus!. It is again very easy to disable Messenger Plus! Live.
Fourth, the user will always be able to disable chat logging, even if the options are locked with a password, by simply unticking "
Enable Logging" in the Plus! menu.
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There is no way to force messenger logging! The user will always be able to disable it.