RE: What is false alarm rate and false positive rate?

["Rob Shein" <shoten () starpower net>]

Martin Roesch did a fantastic way of shedding light on this question.  The
short answer is "neither," but it comes down to this question:  If the IDS
sees an OpenSSL attack go towards an IIS server that isn't using OpenSSL, is
that a false alarm or not?  It's definitely not as useful as it would be as
an alert if the attack were aimed at an actual OpenSSL listener, but it's
not as useless as a complete false alarm that alerts on something that
didn't happen at all.

> -----Original Message-----
> From: Zhuowei Li [mailto:zhuowei () gmail com] 
> Sent: Wednesday, September 15, 2004 2:21 AM
> To: focus-ids () securityfocus com
> Subject: What is false alarm rate and false positive rate?
>
>
> Hi,
>
> I am confused by the terms 'false positive rate' and 'false 
> alarm rate' within the context of intrusion detection. Does 
> anybody about what's the exact definition for these two terms?
>
> Some literatures said 'false positive rate = false alarm 
> rate', which the number of false alarms divided by the number 
> of alarms (true and false).
>
> Other said false positive rate is not equal to false alarm 
> rate, the false alarm rate is the same above definition, but 
> the false positive rate is "the total number of normal 
> instances that were incorrectly classified as intrusions 
> divided by the total number of normal instances"
>
> Who is true, who is wrong within the context of intrusion detection?
>
> Thanks.
>
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