Evil Patronus - ties into Snape's Patronus

[potioncat]

No: HPFGUIDX 141013

(Potioncat, I'm not sure who asked this question:)
>  
> Perhaps this has been discussed before but what evidence is there 
that 
> an evil/dark wizard cannot preform a Patronus Charm?  I have seen 
> several arguments/theory that state if Snape can produce a 
Patronus or 
> send the order a message via the PMS (Patronus Messaging Service) 
that 
> DD invented; it could prove that he is DDM!Snape.
   
> (crypticamoeba gave some information from PoA, quoting Lupin)

Potioncat:
Just before HBP came out, JKR gave answered a question on her site 
about Patronuses. She calls them anti-Dark Arts devices. She says 
the Order would know who sent the Patronus. Only the Order knows how 
to use the Patronuses in this way.

I would cut and paste, but I couldn't get it to work Go to her site, 
to FAQ, then to the poll for FAQ.

I think we should remember, while "we" think the way Snape can prove 
his loyalty is through his Patronus, that may not be correct. I 
think his Patronus could prove he is the one sending information. 
His Patronus form may tell us readers a thing or two. A changed 
Patronus may tell the Order a thing or two.

Personally if I were an Order member, I wouldn't be so certain that 
he hadn't found a way around the ususal safeguards of a Patronus. I 
think he's in a big cauldron of trouble!