1. A method of controlling access to a network resource, comprising: receiving a request to access the network resource, the request including a user identifier; determining whether the received user identifier is stored in a local data store associated with the network resource; and where it is not so determined: determining, from user details stored in a master data store, whether the user is authorized to access the network resource; and where it is so determined: obtaining a password; and storing the obtained password and user details in the local data store associated with the network resource; and archiving from the local data store, user details of users who have not accessed the network resource for a predetermined period of time, and deleting those user details from the local data store.