Please upgrade to 2.1.x here.
The 2.0 branch is no longer being updated.
WhosOnline addon : Bug causing config.php to be over-written?*
This discussion is related to the WhosOnline
I enabled your plugin yesterday on my forum and everything was fine.
This morning the forum stopped working, and I traced it back to the config.php file being overwritten.
I restored the config file, and the forum was fine.
I re-enabled your plugin and within 5 minutes the same thing had occurred, where it seems the config file was being overwritten by an online user who would not otherwise have access to the file.
I can't be certain it was the plugin, but it looks likely.
Just wanted to let you know.