Virus scanning in a computer system

The present invention provides a method, data processing system and program product in which scanning for a virus is improved by prioritizing the scan of executable files, such as applications, libraries, services etc., which are more likely to cause a problem to a computer system, ahead of other files. A priority order is determined free from user input by obtaining information from the operating system which can be used to determine such an order. For example the information comprises details of startup applications and/or launch frequency of installed applications. This enables the virus scanner to prioritize the scan of higher risk files which, if they contained a virus, would otherwise adversely affect a computer system if a prior art virus scan was performed based on an arbitrary search order.