An operating system call, first implemented in Version 7 of AT&T UNIX in 1979, which allows one piece of software (the parent) to observe, control, examine and alter any aspect of another process running on the same operating system. The ptrace call is commonly used to debug running code and can be considered as an active language, infiltrating and interrogating, snooping on and injecting code into living, running processes; an active language projecting a potential process promiscuity within the machine. Ptrace shifts the site of execution and is nowadays commonly viewed as an unnecessary security risk.