That's a big mistake.

     On any Debian system, /bin/sh points to /bin/dash, and dash doesn't 
point to bash. Your system has certainly been hacked.

     Sure, bash can process ash scripts. The problem is the opposite 
isn't true because bash provides a lot of additional features, 
"bashisms", which distros decided to erradicate from their scripts. 
Users are free to write bash or ksh scripts, but portable scripts must 
execute on ash.

     Didier