Google's Andy Rubin hit back at Steve Jobs Monday with a tweet that touted the openness of Google's Android platform.

Rubin, who serves as vice president of engineering at Google, posted a message to the micro-blogging site that might be somewhat confusing to those not familiar with the ins and out of Android coding.

"The definition of open: "mkdir android ; cd android ; repo init -u git://android.git.kernel.org/platform/manifest.git ; repo sync ; make," Rubin tweeted.

Translation: Rubin's tweet includes the commands needed to start compiling a copy of Android on a home Linux machine. He's stressing that anyone can develop for, hack, or even create their own version of Android. The same can probably not be said for Apple, which took a swipe at Google during its Monday earnings call. Chief executive Jobs "dropped by," and eventually called Android "very, very fragmented."

"Google loves to characterize Android as 'open' and iOS and iPhone as 'closed.' We find this a bit disingenuous and clouding the real difference between our two approaches," Jobs said. "The first thing that most of think about when we hear the word 'open' is Windows, which is available on a variety of devices. Unlike Windows, however, where most PCs have the same user interface and run the same apps, Android is very fragmented."

"Many Android OEMs, including the two largest, HTC and Motorola, install proprietary user interfaces to differentiate themselves from the commodity Android experience. The user's left to figure it all out," Jobs continued. "Compare this with iPhone, where every handset works the same."

Jobs also pointed to the various Android app stores – real and rumored – which Jobs said will "be a mess for both users and developers."

"You know, even if Google were right, and the real issue is closed versus open, it is worthwhile to remember that open systems don't often win," Jobs said. "Even Microsoft finally abandoned this open strategy in favor of copying Apple's integrated approach with its Zune player, unfortunately leaving their OEMs empty-handed in the process."

The tweet from Rubin is the only thing the Google executive has ever posted to Twitter. He has not issued any follow-ups since his first message went up about 9 hours ago.

In an interview with PCMag mobile analyst Sascha Segan earlier this month, Rubin said "the world doesn't need another [mobile] platform."

"Android is free and open; I think the only reason you create another platform is for political reasons," Rubin said, in response to a question about the launch of Windows Phone 7. "Why doesn't the whole world run with [Android]? They don't like the people who developed, or 'not invented here,' but [Android] is a successful, complete, vertically integrated free platform. I encourage everybody to use it, but I'm also not under the impression that everybody will use it, which is a good thing, because competition is good for the consumer and if somebody has an an idea for a feature or a piece of functionality in their platform and Android doesn't do it, great."

"What Android is particularly good at that I think some of the other platforms lack, besides being open, is it's really a platform that's enabling a bunch of services," Rubin continued. "When we talk about the Web and we talk about mashups, we're really talking about cloud services."

For more details, read Sascha's full interview with Rubin.