Apple's sandbox for quarantining applications that have been downloaded from the internet or other source. At first launch the system will prompt with a dialog box asking if you want to approve the program launch.

In OS X 10.5 the quarantine was applicable to downloaded applications. In OS X 10.6 it has been further expanded to signed applications and added checking file meta tags against known worms or viruses.

Sometimes, the approve or disapprove is not kept and continuously ask for approval again. To remove the quarantine tag, the following terminal commands are helpful.

To check

xattr -l filepath/filename

To remove

xattr -d filepath/filename