Dumbledore had a number of useful spies

[abhamghp]

No: HPFGUIDX 55820

I was just rereading PoA when something kind of jumped out at me. 
 
In Chapter 10, The Marauder's Map, a number of faculty are 
discussing James and Sirius' relationship in Hogwarts days and the 
secret - keeper that Lily  and James chose.  Fudge states, "Dumbledore, who 
was working tirelessly against You Know Who, had a number of useful 
spies.  One of them tipped him off, and he alerted James and Lily at 
once."  

I wonder who that one spy was, and if this has any significance to the outcome of the entire story.  Does anyone have any ideas?

--galadriel--