We had a bomb threat today

Perhaps at 10:30am, I had seen a police car parked in the drive at the front door of our office building. About 11am, a voice came over the PA system and told us to evacuate the building due to a bomb threat. Then the alarm sounded. At first, I had thought that only our building was affected, but we saw that the building next door was evacuated as well. I left early to get lunch, and I saw that all buildings within sight had been evacuated. When I returned, we soon found that we could go back into the building. While I was out, I heard about the alert at the Whitehouse, and briefly wondered if there was more happening. Apparently, this was an isolated event, although many people and businesses were affected by the shutdown. I was the first back in, and I called our admin guy (a VP, since we are a small company) and told him that we were back into the building. A few minutes past that, I heard the front door, and soon two sales guys were back, as well. We are in a fairly expansive office park in Frisco, TX, at the North end of the Dallas North Tollway. Everyone was speculating, before I went to lunch, why the bomb threat was given. Mostly, the speculation was joking, since no one took it seriously in our company. These days, though, you never know when it might be real (some sort of extremist terrorist, either foreign or domestic).