26Joseph D. Pistone

An FBI agent named Joseph D. Pistone also known as "Donnie Brasco" infiltrated the mob for 6 years to the point that he was going to be "made" but was pulled out because his superiors decided that the operation was becoming too dangerous. - Source
27. The FBI suspected "It's A Wonderful Life" movie was Communist propaganda when first released. - Source
28. A former FBI agent named John P. O'Neill was obsessed with Osama bin Laden and Al Qaeda and warned of the threat of an attack on US soil. He took a job at the World Trade Center in the summer of 2001 and died on September 11th. - Source
29. A set of notes, written in an unknown cipher, was found in the pocket of a dead man (Ricky McCormick) in 1999 and the FBI and leading cryptographers have been completely unable to crack the code. - Source
30. In 1971, a small group calling themselves the Citizens' Commission to investigate the FBI broke into an FBI office in Philly, stole over 1000 documents, exposed the extreme surveillance program COINTELPRO, and then sent these documents to the press, leading to the FBI shutting it down. - Source
31Dante Dears

A wanted pimp named Dante Dears had such a sophisticated pattern lock on his android phone that the FBI was unable to crack it. They had to serve Google with a warrant to try and help them. - Source
32. The FBI and government are allowed to lie in courts for the sake of "national security".- Source
33. Helen Keller's outspoken political radicalism throughout her adult life resulted in the FBI tracking her for years. - Source
34. A hacker named Higinio Ochoa who went by the code name "w0rmer" online hacked an FBI criminal database and replaced it with his trademark image. The image he left behind had GPS coordinates. - Source
35. Mob boss John Gotti would offer coffee to the FBI agents assigned to tail him.
36Richard Jewell

A security guard named Richard Jewell discovered a pipe bomb at the 1996 Olympics in Atlanta and alerted police. He helped evacuate the area, was later considered a suspect by the FBI and presumed guilty by the media. He was exonerated when a homegrown terrorist confessed 9 years later. - Source
37. The FBI tried to infiltrate a mosque in Irvine by sending one of their agents (Craig Monteilh) to incite terrorism. The people of the mosque reported him to the FBI instead. - Source
38. The founder of the FBI (Charles Joseph Bonaparte), who had also served as Secretary of the Navy and US Attorney General was the great nephew of Emperor Napoleon Bonaparte. - Source
39. The FBI sent a letter to Martin Luther King Jr. suggesting that he commit suicide within 34 days or have his sexual exploits exposed to the nation. - Source
40. In 2006, the FBI convicted a crime family using evidence collected by remotely enabling the microphone on a cell phone. This is called a "roving bug."
41Iceland government

In 2013, the government of Iceland asked several FBI agents to leave after they lied to the local government and told them they were investigating terrorist hackers. It turned out they were investigating WikiLeaks. - Source
42. In 2013, after receiving a warning from the FBI on his PC, Jay Matthew Riley turned himself into police for possessing child pornography. The warning was fake and generated by a worm that had infected his computer. - Source
43. John Delorean (designer of the Delorean DMC-12 "back to the future" car) was arrested for conspiracy to traffic narcotics, after being set up by FBI. Delorean was saved from prison after publisher Larry Flynt obtained and released tapes and documents that proved his innocence. - Source
44. In 1980, 4 FBI agents went to the Census Bureau's Colorado Springs office with warrants but were forced to leave. Courts upheld that "no agency, including the FBI, has access to Census data." - Source
45. In 2010, the Walt Disney Company nearly sold the ABC network. The sale was canceled because of an FBI investigation into insider trading. - Source
46Library of Congress

The FBI accidentally registered an internal interrogation manual with the Library of Congress. Anyone with a library card is able to read this secret government document. - Source
47. According to the FBI Director, the FBI is having a hard time filling positions to help tackle cyber crimes because a lot of the nation’s top computer programmers and hacking gurus are also fond of marijuana. - Source
48. The FBI tracks animal abuse just like homicide, arson, and assault. - Source
49. Ronald Reagan gave information on fellow actors to the FBI, and later received political favors from J Edgar Hoover.- Source
50. At the age of 14, Tom Anderson (also known as MySpace Tom) cracked the security of Chase Manhattan Bank and caused one of the biggest FBI raids in California history, but wasn't arrested due to his young age. - Source