CIA insider on what Ottawa shooting means for U.S.

In the wake of the shooting rampage in Ottawa, former CIA deputy director Mike Morell stressed the reality of terror threats at home.

"I am now more worried about a terrorist threat in the United States than I have been for a long, long time," Morell said Thursday on "CBS This Morning." "Because we have the self radicalization problem ourselves; we've got the possibility that ISIS might send fighters here to conduct attacks; we still have al Qaeda in Pakistan, al Qaeda in Yemen and the Khorasan group planning attacks; and we have the fact that what Edward Snowden did has made it much more difficult for law enforcement and intelligence to track these guys. So we are at, I think, a very dangerous time here."

Morell also said he was more concerned about the Canada-U.S. border than the Mexican border because it is easier to cross the Canadian border.

"To stop somebody who has been radicalized in Canada from coming across that border requires that you know about them, that the Canadians know about them and tell us, and that they try to cross that border legally," Morell said. "And you know there's many, many ways to cross that border illegally. So I worry about that."

The only thing the government can do in trying to stop insider terror threats is to monitor extremist websites and see what kind of conversations users are having, Morell said.

"If those conversations start talking about violence, then the FBI can open up an investigation and take a look at that person, but that's a lot of ifs to be able to find somebody who has been radicalized," Morell said.

Canada raised its domestic terror threat level from low to medium Tuesday following "an increase in general chatter from radical Islamist organizations," a spokesman for the public safety minister said.

"I think there's value in raising an alert level because it tells people that you're focused on the threat," Morell said. "I think there's value in raising security around sites that might be attacked, because I think that deters people. I think all of that is positive."