Boston cell phone services were overloaded in the wake of the blast, slowing the city's network dramatically and hampering the investigation in the early going, federal law enforcement officials told CNN.
Unconfirmed rumors began circulating on social media and elsewhere that law enforcement had shut down cell service to prevent more explosives from being detonated remotely. But mobile companies were saying that was never the case, CNN's Doug Gross reports.
"Verizon Wireless has not been asked by any government agency to turn down its wireless service," a spokesman for that company told CNN. "Any reports to that effect are inaccurate."
In other media reports, Sprint similarly denied being asked to shut down service.
Online, Bostonians were being encouraged to stay off of their mobile phones except for emergencies and even open up their wireless connections to help take the load off of the cellular data network.
"If you live or run a business in #Boston near bombsite (please) open your wifi for people to use," tweeted Disaster Tech Lab, an Irish nonprofit dedicated to providing technology to assist in emergency situations.
Authorities have not identified what caused the explosives that erupted at the finish line of the Boston Marathon.
The explosions have killed two people and injured at least 28 others.
If you are trying to find out if a loved one, family member or friend was at the scene, and if they are okay, here are a few resources:
Google's Person Finder
Boston Marathon Runner List
Red Cross Safe and Well