PORTLAND, OR -- The Crook County School District now says it was one of almost a dozen Oregon districts that received e-mailed bomb threats Monday. Officials say the message from a "nerdmail.co" account landed in a spam folder and wasn’t discovered until Tuesday.

Bomb threats Monday caused evacuations, and in some cases school closures around the state. The FBI now says the hoaxes were widespread. "We had over 18 incidents of threats being conveyed to some nearly dozen school districts across the entire state, three synagogues, as well as two of our smaller regional airports and even a small regional airline," says Kieran Ramsey, Special Agent in Charge of the FBI's Portland office. He says clusters of threats are a big drain on law enforcement resources, "We have to assess whether these threats are credible every single time they come in. We can’t simply discount any threat on its face as a nuisance."

The FBI is working with local, state and federal partners, "To determine, ‘Okay; where did this threat originate from? Is there any further potential credibility behind that threat? And, how can we hold them accountable?’" So far, Ramsey says investigators have determined similarities. "Some of the threats used very, very similar language, if not verbatim. In some of the cases, too, we were able to identify an IP address located outside the United States." Although, it’s too early to know whether the person or people responsible are outside the U.S. or just hiding behind the foreign IP address. "We’re early in the investigation, but certainly, some are connected, given the verbiage used and perhaps the commonality of this IP address. Obviously, further investigation will help us suss out whether they are all in fact connected or not."

Ramsey says at least two other states also reported hoax threats Monday, "We know there were a number of incidents out in Ohio and down in Texas. We do not know if those are related, but we’re seeing this across the country."

Ramsey encourages anyone who sees suspicious activity or threats to report it to local law enforcement or the FBI. School threats can also be reported to the Safe Oregon tipline or website. Those caught making hoax threats could face federal charges, punishable by up to five years in prison.