Only new logs created will be encrypted after you set encryption.
You can encrypt existing logs (and more) from the commandline with the logviewer application:
Results of run > "C:\Program Files\Messenger Plus! Live\Log Viewer.exe" /?
Note: strings which contain spaces need to be inside quotes. eg:
"C:\Program Files\Messenger Plus! Live\Log Viewer.exe" /encrypt="c:\my logs\contact1@hotmail.com.txt" /pwd="my password"
In
this post you can find a bat file created by CookieRevised that decrypts all log files in a folder and its subfolders when run from inside that folder.
Edit: you're welcome
Edit2: to make things even more clear i added the full command to encrypt a log. Note: the full path/name to the to encrypt log needs to be specified (just like the full path needs to be entered to the event viewer app). If you use the parameter /overwrite an encrypted logfile with same name (with .ple extension) in same folder will be created, but when a file with that name already exist that one will be overwritten.
("C:\Program Files\Messenger Plus! Live\Log Viewer.exe" /encrypt="c:\my logs\contact1@hotmail.com.txt" /pwd="my password" /overwrite).