The present invention provides both method and apparatus for enhancing a user's network security. For example, it may be used to prevent phishing attacks being effected via the internet. A number of legitimate network addresses along with associated data are stored. Subsequently, analysis is carried out on any data transmitted between the user and a remote site to determine if the transmitted data is related to the stored data. If it is found that the data is related, user access to the remote site is denied unless the remote site's address is one of the stored network addresses. This provides more security than was previously available since it protects the user against attacks from sites that were not previously known to pose a threat.