Disable “application downloaded from the internet” message in Mac OS X
You can remove the “Blah is an application downloaded from the internet. Are you sure you want to open it?” on a per application basis by using the following command:
xattr -d -r com.apple.quarantine /Path/to/application/

If you want to remove the that warning message from all in your ~/Downloads directory, you can type the following command:
xattr -d -r com.apple.quarantine ~/Downloads
Remember this method only effects items you choose to specify. If you want to disable this message from ever appearing again for any applications downloaded, learn how to permanently disable the file warning dialogue.
Related articles:
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- Show Download History List of All Files Ever Downloaded Within Mac OS X
- Hide SMS & iMessage Previews from the Lock Screen on iPhone
- Fix the “App can’t be opened because it is from an unidentified developer” Error in Mac OS X

Thanks it works !!!
Perfect! Now how do you reverse this if needed?
option -r not recognized
usage: xattr [-l] file [file ...]
xattr -p [-l] attr_name file [file ...]
xattr -w attr_name attr_value file [file ...]
xattr -d attr_name file [file ...]
The first form lists the names of all xattrs on the given file(s).
The second form (-p) prints the value of the xattr attr_name.
The third form (-w) sets the value of the xattr attr_name to attr_value.
The fourth form (-d) deletes the xattr attr_name.
DOESN’T WORK IN LION.
Yet another defect in this POS. Lion is a huge regression and massive embarrassment to Apple.
What an affront to customers.
Works in Lion for me. Required admin login in Terminal. Quit yer whinin’, What Haveyou.
[...] OS X Daily has provided a [...]
This don’t seem to work on 10.5.8 as there is no switch for recursivity.
To be more precise, it will fail because 10.5.8 doesn’t understand the -r option. There is no man page, but there is help (works on 10.6 and 10.5) using:
xattr -h
This command will do it under 10.5
find folderpath -print0 | xargs -0 xattr -d com.apple.quarantine
where folderpath is the folder you want to recurse into eg:
find ~/Downloads -print0 | xargs -0 xattr -d com.apple.quarantine
worked for me on 10.7.3, but i had to preface it w/ sudo:
> sudo xattr -d -r com.apple.quarantine /Path/to/application/
I keep getting a “no such file.” I believe this is because I am using an incorrect path to the application? Is there a quick and easy way to find the correct path? I tried /hard drive/applications/firefox and every conceivable variant to no avail.
[...] list even works if you have file quarantine turned off for files and apps, thanks to inket for verifying [...]
[...] Apparently, marking the file with an extended attribute wasn’t enough for this ‘security’ feature, so Apple decided they should also keep a log, dating back all these downloaded files. That is a SQLite DB that OS X use to show the download URL in the alert window when the file is executed. And it keeps information about downloads by all kinds of applications (skype, cyberduck, email attachments…), not just browsers. This is a mechanism supposed to protect us users form unintentional execution of malware. Apple didn’t seem to mind that the DB will continue to collect data even after file quarantine was turned off for files and apps. [...]