lets say a game isn't copyrighted, and someone takes the game then "hacks" it, then renames it and places it back on their site. Would there be any legal issues with this? One example is line flyer. (modded version of line rider).
Just because it does not say "Copyright" on the game, does not mean the creator doesnt have and own the rights. Changing the game may be ok, but attempting to make it look like your own is a whole different story.
Precisely, if it was also open-source and not claiming ownership, it'd be fine. Best to actually get permission from author first though.
Are you sure about this? Copyright exists as soon as a creation takes a fixed form, whether or not it has copyright notices plastered all over it. If there's no FAQ or readme with this information, the only way to know for sure is to ask whoever built it.