Ariane 5
The Ariane 5 rocket exploded 37 seconds after launch.
A software conversion error occurred.
A 64-bit floating point number was converted into a 16-bit integer, which caused an overflow error.
The software used was copied from Ariane 4 rocket without proper testing for Ariane 5 conditions.
Loss of about $370 million.
Never reuse code without testing under new conditions.
Knight Capital Group
A deployment mistake caused the system to start buying and selling stocks randomly.