I have received a helpful response from the IB admin,Brandi.
The investigation reveals that the source of the concern is a large plumbing ad,hosted in the Ukraine on this page :
http://www.pprune.org/jet-blast/5259...es-insane.html
I have AdBlock installed and can't see the ad,but as soon as I went to that page,the IP blocker on Malwarebytes triggered.