Alien characters

I've recently discovered some files + folders labelled with strange symbols that have infiltrated my prefs folder. An example is "åÕê÷òøˇ’†~" (in case they don't show properly here - they are a few of those foreign-language accented characters mixed with mathematical symbols etc).

I only found them when backing up to my external HD - they were flagged up as unable to be copied. I just deleted them from my prefs but new ones reappear. They don't seem to do anything but they are a nuisance.

Anybody have any ideas where they come from?

Thanks
The Joolster