Court documents have revealed new details about the agency's high-tech investigative techniques in the case of "Mo," allegedly an Iranian who has made threats of mass murder against US citizens. The scale of the FBI's hacking effort is hard to pin down, but Mo is just one of a handful of suspects known to have been targeted.
Unfortunately for the feds, their hackers haven't turned up much about Mo.

The FBI bungled the installation of its malware after the suspect's email address was misspelled, then had to rewrite part of the tool after an internal software update.
Finally, the agents successfully emailed Mo a link that would install the malware, which he clicked on. But the tool malfunctioned and "never actually executed as designed." Investigators learned only that Mo appeared to be in Tehran. No wonder the FBI is always recruiting at DefCon.