How to Suppress Repetition of Warnings That an Application Was Downloaded From the Internet on Mac OS X?

To remove the quarantine alert you can run the following command in Terminal:

xattr -d com.apple.quarantine /PATH/TO/APPLICATION

You may need to run this is an administrator depending on the permissions on the resulting application (as you said you don't run as administrator). If the application has permissions set that you can't remove the metadata with your user account it explains why it comes up every time. You can either run it as an administrator on your computer or run the command above as an administrator. (Use su admin_name if necessary)

To stop this from happening in the future, go to Terminal and type this (hitting Return afterwards):

defaults write com.apple.LaunchServices LSQuarantine -bool NO

Source: MacWorld

Or — simpler yet — download Secrets and search for “quarantine.”

http://www.macosxhints.com/article.php?story=20071029151619619

A Vista-esque feature of OS X 10.5 is that it tags web downloads (not just those from Safari) as such, and then warns you about running downloaded apps. Archived (e.g. zipped) files inherit the tags from their tagged container.

Link is to discussion of issue and a few scripts and C++ strings you can run to change the behavior permanently.

Not sure if these are going to work with 10.6

Building off of something in the answer from Chealion above I found a simpler solution (that worked for me) that didn't require that I disable all warnings.

This from Chealion:

If the application has permissions set that you can't remove the metadata with your user account it explains why it comes up every time. You can either run it as an administrator on your computer or run the command above as an administrator. (Use su admin_name if necessary)

So instead of running the command from Chealion just changed the ownership of the application that was causing problems using "chown"

chown username \Applications\ApplicationName.app

this issue seemed to be caused by an application that was installed by an administrator when imaging my computer. After I changed ownership the warning didn't reappear.

If there's a file named com.apple.DownloadAssessment.plist in your user's Library/Preferences folder, it will override the global defaults for which files Safari considers "safe." You can also use this technique to make currently-safe files treated as unsafe. In fact, there are four different top-level risk categories:

1. LSRiskCategorySafe - Auto-opened after download, if Safari has this option enabled.
2. LSRiskCategoryNeutral - A neutral file won't be auto-opened, but there won't be a warning about its contents, either.
3. LSRiskCategoryUnsafeExecutable - All executable files fall into this category, and you'll see a warning when you attempt to download one in Safari, Mail, etc.
4. LSRiskCategoryMayContainUnsafeExecutable - This covers 'container' formats such as disk images and archives. If Safari/Mail can see the contents of the container and determine they're all safe, then no warning will be generated.

For full information, I refer you to this page.