1. A processing device for executing an instruction sequence, wherein the processing device comprises a status register arranged to provide a status word, a set of valid status words, and a status flag monitor, wherein the processing device is arranged to update the status word in response to execution of an instruction, wherein the instruction sequence comprises a subsequence of one or more selected instructions, wherein upon execution of one of the selected instructions by the processing device, the processing device is further arranged to trigger a status check by the status flag monitor, wherein the status flag monitor is arranged to: to verify whether the updated status word in the status register is in a set of valid status words, wherein the processing device is arranged to provide the set of valid status words to the status flag monitor; and to assert an alert action if the updated status word is not in the set of valid status words.