In the aftermath of Tuesday's mysterious zone transfers from
netcraft.co.uk, and following up on a suggestion from Russ
Sutherland, I changed my named.boot to admit zone transfers
only from my own network and from the official U of T secondaries:

xfrnets	128.100.104.0&255.255.255.0
xfrnets 128.100.100.128&255.255.255.255 128.100.102.201&255.255.255.255
xfrnets 128.100.1.1&255.255.255.255 128.100.2.2&255.255.255.255
xfrnets 16.1.0.19&255.255.255.255 204.123.2.18&255.255.255.255

These are, in order:
- my network
- dense.utcc snort.utcc
- two different addresses for bay.cs
- uucp-gw-2.pa.dec.com uucp-gw-1.pa.dec.com

Since doing that, I have also received (and my named has
rejected) zone transfer requests from these systems:

128.100.102.28	stamp.utcc
128.100.102.252	gated.gw
128.100.100.3	ugw.utcc
128.100.100.1	gpu.utcc

Why are these systems doing zone transfers?  Are they valid
secondaries worth declaring in my NS records, or is there some
other reason for the zone transfers, or is it just pointless
hackery that I should ignore (and continue to refuse)?
(I can guess some of the answers for some of the systems,
but it seems worthwhile to have the official answers displayed
in public.)