Provided is a technique for Input/Output scanning. A storage controller receives I/O requests from a host system, having an operating system, directed to at least one storage unit, wherein the storage controller manages I/O access to the at least one storage unit. A scanner program is loaded before executing any I/O requests directed to the at least one storage unit and the scanner program is run to check for code identified in code definitions in I/O requests directed to the at least one storage unit before and after the host operating system is loaded.