What sheer nonsense. Do you work for a harddisk vendor by
any chance? An external harddisk for your shared files buys you absolutely no security whatsoever.
The only reasonable and workable solution is to use a
dedicated account for LimeWire and preparing file/directory
permissions accordingly. If that's too hard for you, forget
about security altogether, you're just wasting your time.

Anything else is nothing but snake oil. Cheers.