How does nessus know exactly which application is running

[alan donald <netquantum_at_yahoo.com>]

(This question is somewhat related to one my earleir
posts.)

I am a bit confused. I dont seem to understand how
nessus is knowing which application is running. Since
it has to know this information in order to launch an
exploit. 

Is it just matching a banner
OR
does it have a database of responses for each
application like maybe nmap does. 
OR
It is fingerprinting the application in some other
way.


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