That's what the DHS has been telling us for a few years now (probably the greatest achievement of Janet Napolitano's tenure). That's what happened in Miami this week when a couple of Muslim women began showing up at area synogues and asking questions about when there would be congregations.
CAIR (Florida) is also following the story.
Would I have called the police? Given the situation we live in, yes. Let them investigate and determine if there is a threat or not. This should not be used as another excuse to yell, "Islamophobia". I note that the Florida chapter of CAIR is not accusing anyone of this as yet, just reporting it.