Methods and apparatus for ensuring the computer security of users of a computer system are described. A user is allocated a security grading relating to how secure their computer system (2) is, for instance in terms of anti-virus software, firewalls and up-to-date security patches. Methods and apparatus (10, 12) for providing a security grading of a user's computer system are also disclosed. Users without a security grading or with low level security grading may then be accorded only basic access to the data or functionality of another computer system (8), for instance such as on-line banking services or the like. This ensures therefore that those users that take responsibility for their own security are allowed full access without undue security protocols whereas users without proper security do not have so much access.