1. A method of installing and/or un-installing software in a network, the method comprising: on each of a plurality of networks, accessing a network management system of the network, the network management system storing metadata comprising at least the identities and command lines of software installed using installation systems of the management systems, and obtaining the metadata for items of software run on the network; comparing the metadata of instances of the same software on different networks; and for those instances of the same software having the same metadata on different networks, storing in a database the metadata of the instances of the software; using the metadata stored in the database to automatically install or un-install software in at least one of the networks; and wherein the network management system of each network has a database storing an application execution history table and an application package table which contains metadata comprising at least the identities and command lines of software installed on the network, and the metadata for items of software run on the network is obtained by running on a computer of the network a program configured to compare fields of the application execution history table with fields of the application package table.