Before we begin, I'd just like to say this ...

That weird square that looks like an empty crossword puzzle is actually a kind of bar code, called a QR code. QR stands for “;Quick Response,”; and it was designed to be quickly read when scanned with a camera phone. The idea is to save people the tedium of tapping in information by hand, or rather, by thumb.

QR codes can contain URLs, phone numbers or regular text like the “;secret message”; above. In Japan, where the format was created, QR codes are widely used on signs. Now they're popping up in Honolulu and across the United States.

More than a dozen iPhone apps can handle the codes, but I'm focusing on the three most popular and well-reviewed free ones in the App Store. After rigorous testing in the App Attack Labs (i.e., my newsroom desk) and in the field (Ala Moana Center), I've narrowed it down:

» QR App: The most popular and simplest program for QR codes in the App Store, this utility does just what it says. Just point and ... that's it, really. If you line up the shot with a clear image of the code, you won't even have to click the iPhone's camera button. If the decoded data contains a URL, you have the option to open it in Safari. QR App also keeps a history of codes you've scanned. Too bad about that URL, though: www.qrapp.com.

» QuiQR Free: This app holds your hand a bit more, in a useful way. After you click the “;scan”; button, an overlay on the image shows how best to line up the code block, while doing away with the camera button. This saves time on failed attempts to decode seemingly good shots.

Normally I wouldn't applaud removing the option for a human to override a computer (it never goes well in movies), but the idea is to give the program something it can definitely work with. You can also select an image from your iPhone's camera roll to decode. quiqr.posterous.com

» 2D Sense: The most ambitious program tested reads a number of code formats besides QR and keeps a record of the code images you've scanned, as well as their contents; a nice touch. The app works with the 2D Sense site, where users can create QR codes, as well as in the other supported formats.

The company, based in Lithuania, has an international focus, and some of the English is broken, not that it's a criticism. What is a problem, though, is that 2D Sense is the slowest and most bug-ridden of the programs tested. Scanning a code works by point-and-click, with the advantage of allowing you to move and zoom the resulting image to maximize the code. However, decoding is far from “;quick”; and can take up to several seconds to finish. It also crashed frequently in testing, taking us back to the iPhone's home screen. www.2dsense.com

We were most impressed with QuiQR Free for its ease of use and reliability. QR App is a close second when it comes to QR Codes, but its bare-bones interface can make scanning a chore. 2D Sense has some great ideas—the range of other code types is a welcome addition—but its slowness and instability means it's not yet worthy of a download.