Misprision of felony was an offence under the common law of England and was classified as a misdemeanour. It consisted of failing to report knowledge of a felony to the appropriate authorities. Exceptions were made for close family members of the felon and where the disclosure would tend to incriminate him of that offence or another.
With the development of the modern law, this crime has been discarded in many jurisdictions, and is generally only applied against persons placed in a special position of authority or responsibility. In this case, the offence of misfeasance in public office or malfeasance in public office may be considered instead. For example, corrections officers who stand idly by while drug trafficking occurs within the prison may be prosecuted for this crime.
It has been abolished in England and Wales, in Northern Ireland, in the Republic of Ireland, and in New South Wales and other Australian States and Territories, but has often been replaced by a statutory offence.
United States federal law
"Misprision of felony" is still an offense under United States federal law after being codified in 1909 under 18 U.S.C. ยง 4:
Whoever, having knowledge of the actual commission of a felony cognizable by a court of the United States, conceals and does not as soon as possible make known the same to some judge or other person in civil or military authority under the United States, shall be fined under this title or imprisoned not more than three years, or both.
This offense, however, requires active concealment of a known felony rather than merely failing to report it.
If one knows that one is a target of a Federal investigation, it is illegal under the Sarbanes-Oxley Act to erase one's browser history intentionally. Khairullozhan Matanov was prosecuted for erasing computer records about his friends, Dzhokhar and Tamerlan Tsarnaev; he pleaded guilty to a lesser included offense in 2015.
The Federal misprision of felony statute is usually only used in prosecutions against defendants who have a special duty to report a crime, such as a government official.