VProtect is a module which will prevent any of the known viruses from
loading via a !Boot file. It will also prevent further infection by the
Module virus.

You should copy it into the !System.Modules directory, and set up a !Boot
script to ensure that it is loaded.

The commands to put in the !Boot file would typically be:

rmensure vprotect 0 rmload system:modules.vprotect
rmensure vprotect 0 error VProtect has not been loaded

However, it is quite likely that the computer does not yet know where the
!System directory is, so you may instead have to use the full path to
!system, eg

rmensure vprotect 0 rmload adfs::4.!system.modules.vprotect

If you are using RISC OS 3, it will automatically include a suitable command
to load itself in the Desktop Save file.