In my experience, anything by, with or from Computer Associates is suspect. That is, of course, a subjective and purely personal opinion, based on a series of bad experiences with their products and their people.
But I think that Mutt has the answer - a change of source IP address for
www.pprune.org or .com probably confused the CA product.
If in doubt, ping
www.pprune.org - the correct IP address is 67.201.16.181.
Check also loading 67.201.16.181 directly into your browser.
www.pprune.org should appear.
SD