E-mail messages or computer files are scanned to identify embedded internet addresses. These embedded internet address 18 refer to data that may be retrieved via the internet. This data is pre-emptively retrieved and scanned for malware even though it has not been requested by a user. If the data is found to be malware-free, then a record of this is kept. If a user subsequently seeks to access the data associated with the embedded internet address, then the stored data may be referred to and if the internet address is found and the data associated with that address is unchanged since it was previously scanned, then that data may be supplied to the user without the need to be rescanned.