Doesn't seem to work. I installed it under Mac OS X 10.4.5. The first time I ran it, when I tried to save the list of blocked sites, it asked me for my administrator password multiple times and never was able to authenticate, even though I'm positive that I was typing the correct password. I quit the program, re-launched it, and it would not relaunch because my etc/hosts file had been deleted. Something is very wrong here.