Snape and the Order

[steffy07]

No: HPFGUIDX 94062

This may have been discussed before, but I have a question...

In OOTP, if Snape is spying on LV for the Order (which I believe he 
is), and the Deatheaters know he works at Hogwarts, shouldn't he be 
expected to spy on Dumbley-Dore and Harry for LV?  Is he passing 
false information to LV?  If so, why hasn't he been discovered yet 
by the DE and LV?  Wouldn't you be suspicious if all the information 
a spy told you turned out to be false?

Just wondering everybody's opinion...

Steffy