Mac OS X has long had a "quarantine" feature, which alerts users when they open files that they downloaded from the web, or received as attachments with e-mails, or received via iChat file transfer. With the update to OS X 10.7.4, which Apple released yesterday, there is a new dialog:
This main difference is the new icon, which is the same icon used for the Security & Privacy preference pane. This icon may become a new standard for security-related alerts on OS X, and may be more effective than the previous icon, which was simply a larger version of the yellow ! icon shown in the screenshot above.