Jack 1000 wrote:Or by selecting "Check For Updates" or something similar from within a trusted program.
Even that's not always a reliable method. Take the recent Shareaza takeover for instance: the Shareaza.com domain was taken over, the software replaced with a malware-ridden version, and since the old versions are configured to check for updates on Shareaza.com, they offer to update to the malware version. The scammers also filed to trademark Shareaza, so the situation is pretty grim. You can help this excellent open source project with legal advice or donations or what have you at http://shareaza.sourceforge.net/
Anyway, I don't mean to go off-track, I just thought that was worth mentioning.