Pvt. Bradley Manning managed to bypass security of the US army computers. During investigation of theft of more than 150,000 top secret files it was revealed that he carried data on a disk labeled as a Lady Gaga music CD.
Use of portable disks, including USB flash disks is strictly prohibited on all computers of the US army. However, a music CD was not noticed and Manning could provide key information on American diplomatic dealings to other people without anybody noticing.
Manning was originally arrested due to investigation of a published video of unsuccessful attack of an American helicopter. Apart from other civilians, the Reuters journalists died during the attack. The more serious problem in form of a threat to the US national security was revealed later by accident when a former hacker denounced him. Manning told the hacker about his dissatisfaction with American foreign policy.