Jeremy Breef-Pilz, KB1REQ, a ham radio operator working communications in the finish area, reported on on Twitter that all hams at the Marathon are safe:
"@KB1REQ: All #HamRadio
volunteers for the #BostonMarathon are safe. We complied with evacuation
orders, not an incident for us to be involved in."
(Tnx to KB1REQ via WA3PZO)