Whenever you download an HTML file from the internet (say, in a zip archive), the first time you open the file in OS X you get a warning something like "this file was downloaded from the internet and may do horrible things to your mother, are you sure you want to open it"? Once you click OK, you can open that file again without further harassment.

Is there anyway to quickly mark a group of these files as safe so the warning doesn't show up the first time you open them? 

My specific use case is I've downloaded a large number of HTML files that I'm searching through, and then using the "open" command to open. If I try to open five files at once I get five warning dialogs, which is tedious and irritating.