Comment 2 for bug 688736

We are trying to protect the Ubuntu desktop from malware. One of the popular malware attack vectors is a "Drive by download": to have a user unknowingly download an executable file and hope they double click on it later at which point the malware is executed.

Since Ubuntu software is normally installed through signed repositories using the Ubuntu Software Centre, there is no reason to encourage the Windows-type behaviour of downloading a random piece of unsigned software from the Internet and executing it. Thus, random downloaded files are not executable by default, and executing them should be reserved for advanced users who know the implications of doing so.