Flash on PowerPC is horribly insecure as it hasn't been updated since version 10.1, but since some sites like the BBC require it for their videos, some people insist on still using it. However, more and more sites are requiring version 11.5, and since we're no longer getting updates, users have to rely on a version string hack to get their 10.1 plugin to spoof itself as 11.5. MacRumors Forum member Wildy has made the latest hack available here. Again, it's the 10.1 plugin merely spoofing itself as 11.5.
I don't personally use flash anymore, but to make it slightly less insecure you should uninstall the plugin from your system's /Library/Internet Plug-Ins folder and put it in ~/Library/Internet Plug-Ins (the ~ denotes your home folder if ya didn't know). That way it's not installed system-wide for other users to stumble on. Also, you should run a browser with a flash blocker so you are only loading videos you specifically click on. Camino has a flash blocker in its preferences, Safari/Webkit has Click-to-Flash, and TenFourFox has the Flashblock or NoScript add-ons. None of this is guaranteed protection, keep in mind.
If you want to move completely beyond flash as you probably should, you can go over to Life without Flash: share your tips and tricks, a thread started by B-G. Also, for Linuxers, there's this Crunchbang forum thread with some useful info. And there's also my favorite little tool, quvi.