HOUSTON -

Threats against schools are not a new problem, but they are changing and school districts are having a hard time staying a step ahead.

"I heard it started as, like, a text," one student said about a threat.

With increasing frequency, threats of violence are becoming a genuine disruption.

"I've seen a lot of cops in there," one student said about a response to a threat.

In 2013, KPRC Local 2 has covered 11 separate schools targeted by violent but empty threats. Many of the threats have been posted and passed along on social media websites, like Facebook and Twitter.

In most cases, police and administrators lock down buildings and curtail student movement. It's a massive expenditure of energy and resources. During those tense minutes and sometimes hours, students aren't learning.

The Spring Branch Independent School District said it has asked for the FBI to help to investigate threats made against its schools, but it has also hired tech-savvy investigators.

"Over the years I've been in law enforcement, things have changed," Spring Branch ISD Police Chief Charles Brawner said. "The new concern now is social media and how it's being used with threats against schools."

Investigators said they may not be able to stop someone from making a threat, but they need to track down whoever does make one.

Terroristic threats can be prosecuted in Texas as either misdemeanors or felonies with penalties of up to 10 years in prison and a $10,000 fine.