Binary package hint: amsn
Currently, if your version of aMSN is not the latest version, you get a prompt to download the latest version directly from the aMSN website, even if aMSN has been installed from the official Ubuntu repositories. For applications installed via the package manager, updating should not be handled by the application, but instead, by the package manager. If aMSN has been installed from the official repositories, it should not prompt the user to download the latest version (much in the same way that Firefox does not check for updates itself).
Currently, the only way to stop aMSN from prompting the user (if the newest version isn't included in the repositories), is to download aMSN manually, which may not be easy for some users.
It seems that there is a preference to enable checking for new versions on startup (Automatically check for new versions on startup), but it is right at the bottom of the advanced tab in the preferences window (you have to scroll down on my 1600x1200 monitor. Maybe this should be unchecked by default.