Richard Clayton wrote:
we're grateful (albeit a little embarrassed) for the consideration given
to one of our figures by Ted Wobber (MS Research) who has pointed out a
tenfold error in our sum involving an 0.0023% response rate :-(
Well that's a little better. For hashcash. Of course it would still be
desirable to have a factor 1000 margin of safety or similar.
we'll be revising our text accordingly -- since this will weaken our
statements about the "economic argument" ... though it does _not_ affect
our analysis based on use of zombies
I'm wondering about the zombie argument. So clearly it is valid,
spammers can and do obtain zombies through viruses etc. However it is
somewhat demanding of a threat model on any anti-spam system to say that
it should remain secure if the spammers 0wn some significant fraction of
user machines.
For example consider the following anti-spam systems and the effect of
owning the machines:
- signature based / verified sender -- broken, spammer just installs
malware on zombie which abuses the users credential
- white-list based -- broken (more limited perhaps can only reach the
set of users who have white-listed the zombie owners) spammer harvests
white-listed pairs of addresses and optionally sends from the same
zombie harvested from. (You see this with the virus payload that sends
from random pairs from address book -- where you frequently receive
virus propagation and/or spam mail from people who's email addresses
your recognize.)
likely similar problems apply to most other anti-spam approaches if the
person you are defending against 0wns lots of machines.
Adam
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