'nessus' like vulnerability scanners; nessus has gone commercial with
a non commercial free trial.
A search for open source lic. equivalent, brought up this link that lists a few.
http://alternativeto.net/software/nessus/
I was aware of openVAS but have not used it at all. Never heard of
the other listed products.
Please share your experience if you have used any of them.
TIA,
-- Arun Khan