The emphasis that AgileBits has traditionally placed on security has also been carried over to the new version of the app; all data is encrypted using the 256-bit AES standard, and a new special digital signature helps prevent tampering. More importantly, the user interface strikes an excellent balance between security and convenience: the default timeouts are calibrated so that you don't have to input your master password too often while still taking effect soon enough that your data doesn't remain accessible for too long.
New in version 4 is also a feature called a Security Audit that causes 1Password to go over your entire password database looking for potential security issues, such as weak passwords or logins that you haven't used or changed in a long time. If you happen to be a longtime user of the app, chances are that you'll benefit from this functionality--I tend to be fairly cautious with my credentials, but still ended up changing about half a dozen long-forgotten logins after going through an audit.
As good as ever
The new 1Password is every bit as good as its predecessors and represents exactly the kind of update that I was hoping for from the folks at AgileBits. The app is unobtrusive (unless it needs your attention, in which case it's not timid about asking for it) and feels both lightweight and responsive. In my brief testing, it has also been very stable on both OS X Mountain Lion and even on the latest Mavericks betas, performing without any glitches or crashes.
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