The condition wherein the data transferred to a buffer exceeds the storage capacity of the buffer and some of the data verflows into another buffer, one that the data was not intended to go into. Since buffers can only hold a specific amount of data, when that capacity has been reached the data has to flow somewhere else, typically into another buffer, which can corrupt data that is already contained in that buffer.

Malicious hackers can launch buffer overflow attacks wherein data with instructions to corrupt a system are purposely written into a file in full knowledge that the data will overflow a buffer and release the instructions into the computer instructions.