A method of administering a network comprises the steps of: detecting the occurrence of a triggering event alerting an administrator to the presence of a user entity on the network, the triggering event being selected from the group consisting of: (i) allocation of a network address to the user entity; (ii) alteration of the user entity's network address; (iii) an action by the user entity causing resolution between a network address and an identifier; (iv) association of the user entity's network address and an identifier. Upon detecting such an event, the user entity having the network address is scanned for vulnerabilities by sending at least one outward packet to it, for example seeking to establish a connection on a particular port, and the response, if any, is then used to determine whether is vulnerable to known malicious code.