Abstract: A computer 2 is booted with a removable physical media 10 which bears a clean non-installed operating system. Network support code is also loaded from the removable physical media 10 and used to establish a connection with a remote computer 6, 8. Malware detection files are then downloaded from the remote computer 6, 8 and used to perform a malware detection operation upon the computer 2. Thus, the removable physical media 10 necessary to perform the clean boot may be distributed in advance of a malware outbreak whilst the downloading from a remote computer 6, 8 of the malware detection files ensures that the most up-to-date versions of these files will be used when the removable physical media 10 is employed to conduct a clean boot and trigger a malware detection operation in a malware outbreak situation.