It’s also been #1 in June 2013, when it also spiked over 1,000,
and in July 2012, when it spiked to 90 spam messages a month.
In all three months it had a background noise volume of around 10 between spikes. And in all three months the spikes didn’t last very long. So it appears U-PGH-NET-AS has some sort of chronic problem with letting spam out, but UPMC does notice whenever it gets bad and fixes it pretty quickly. This latest #1 was actually worse for this ASN, however, since the previous two times it spammed about a third of the top 10 total, and this time it spammed 42.1%.
Top volume is also up an order of magnitude, from 90 to above 1,000. UPMC seems to have something to fix.