The latest Handler's Diary from the Internet Storm Center (sic) has a useful note on the verification of downloaded software. I found this Linux Online article especially interesting.
And yes, I have to confess that I have taken things on trust for far too long and have only been following these procedures myself for a relatively short time.
Think security - they're out to get you!
Published Monday, 30th May 2005, last updated on Sunday, 24th September 2006.
