Cold War Software Bugs
Here’s a report that the CIA slipped software bugs to the Soviets in the 1980s:
In January 1982, President Ronald Reagan approved a CIA plan to sabotage the economy of the Soviet Union through covert transfers of technology that contained hidden malfunctions, including software that later triggered a huge explosion in a Siberian natural gas pipeline, according to a new memoir by a Reagan White House official.
A CIA article from 1996 also describes this.
EDITED TO ADD (11/14): Marcus Ranum wrote about this.