Functionality unknown to the legitimate user, which provides secret access to data or a change in functionality contained in software or hardware. The introduction of a backdoor in a software without the user's knowledge turns the software into a Trojan horse
Buffer overflow, buffer overrun (BOF)
An anomaly that occurs when software writing data to a buffer exceeds the buffer's capacity, causing adjacent memory locations to be overwritten. Buffer overflows can be exploited by attackers to modify a computer's memory in order to undermine or take control of a program's execution.