Cleaning up after a worm or virus is relatively straightforward. If a software manufacturer provided an infected file, it can be replaced with a clean copy. Private files cannot usually be replaced but it is possible to delete the infected portion or overwrite it with something harmless. As well as detection patterns, the scanner's master pattern list can contain instructions about what files are normally infected by a particular piece of malicious software and how to clean them up. Like the patterns, security technicians create these instructions, normally at the same time as the patterns themselves.