.htaccess bypassed by PDA!

Help! Folders on my website that appear to be password-protected (using
..htaccess) when viewed from a standard computer seem to lose their
password-protection when I view them from my PDA. This is a serious security
hole and I desperately need a fix, but can't find anything anywhere which
even reports the problem, let alone suggests a way to get around it. Any
help gratefully received.