Microwave ovens and Project Phoenix S-band - how can they tell?

Just read the articles at seti.org on the ongoing observations
by Project Phoenix at Arecibo.  All great stuff, but in all my
years of reading about SETI, I had not come across Microwave
Ovens as being a major source of RFI.  Yet MOs were
implicated 3 times in those SETI Institute articles.

I'm curious:  how are they able to differentiate MOs from other
users of the 2.4 GHz band?  I know of many people [1] who
abuse the airwaves by pushing their 802.11b wireless
networking systems to ridiculously high powers and range.
Surely these are the culprits of the 2.4 GHz noise?


[1] http://www.pbs.org/cringely/pulpit/pulpit20010712.html