A method of scanning data for viruses in a computer device, the device having a browser for rendering the data for use. The method comprises storing the data in a buffer memory accessible to said browser and creating an instance of a browser plugin, said plugin providing a virus scanning function or providing a route to a virus scanning function. The data is scanned for viruses using the instance of the plugin and, if no viruses are detected in the data, it is returned to the browser for rendering. If a virus is detected in the data, rendering of the data is inhibited.