Computer device and method for controlling access to a printer

A method of controlling printing on printing services 50L, 50N, accessible from a primary user account 110 on a computer system comprises isolating untrusted content files 221 in a sandbox 200, formed as a content isolation environment by a secondary user account 210, which does not have access to the printing services. Printing may be controlled by an agent 500. The agent may decide, having examined an intercepted print request from the secondary user account, to allow printing to a staging file 511. The staging file is then stored in a location which may be accessible from the primary user account. Once a notification has been received indicating that the printing to the staging file has been completed, the staging file can then be printed using the printer services accessible from the primary user account.