Heya!
This seems interesting so I gave it a quick try, and it looks like it breaks FINAL FANTASY XI Online in quite the interesting way.
After logging in on the PlayOnline Viewer, which is used to log in on FFXI (think of Steam before Steam et al.), it claims it needs an update even though that's not true. It proceeds with downloading a patch-related file, but then complains:
“Some problems occurred in HDD data. Please check installation status.”
I did not yet look into it more, but figured I'd mention this here already.
Thanks!