Lowest version of Apache webserver that's not vulnerable on Tru64 V5.1

Hi,

I'm currently running Apache/1.3.26 on Tru64  Ver 5.1
& the security guys' Nessus scan reported this is a
vulnerable version.

I got from a HP website the following Apache webserver:
Tru64Apache_sws_v6_5_5b.tar.gz


A couple questions with the above downloaded version :

a)
How is it this one has such a high version number of 6.5-5?
I thought the latest Apache version is only 2.x?

b)
Can I just upgrade my current 1.3.26 version directly to
this v6_5_5b that I got?

c)
Is this v6_5_5b a vulnerable version?



Regds
Goh 






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