Some federal courthouses ban smartphones because of fears that could be used as weapons by terrorists.

A memo issued last week by the Administrative Office of the U.S. Courts outlines the dangers, Wired’s Threat Level blog reports. “These common devices present security issues because some can be and have been converted for use as weapons, including explosives,” the report says.

The report explains other dangers: Smartphones can be used to secretly record or transmit videos of court proceedings, and they can be used by jurors to research case details on the Internet.

Courthouses vary in their policies, according to Threat Level. In San Francisco, for example, Wi-Fi connections allow access to the Internet in courtrooms, and live blogging and tweeting is common there.