Lose Files, rkhunter -c, doesnt show any rootkit, healthy hard disk

[perljpes@gmail.com]

Hello to list,

There is a problem to a computer,
It loses files, not very often, files downloaded from internet.
rkhunter -c,  doesnt show any rootkit, smartctl --all /dev/sdX , shows a 
healthy hard disk.

Any suggestion?

Thank you Nikos Macheras