iPhone 4 or 4S? A screenshot of Siri on an iPhone 4. Image: Jon Snyder/Wired.com

A new hack delivers the Siri digital assistant to jailbroken iPhone 4 units, but we advise would-be tinkerers to think long and hard before acting on the invasive software surgery. You might think you know your way around an iPhone hack, but this one has trouble written all over it.

This downloadable version of Siri, called H1Siri, is available in the Cydia app store. The language accompanying the 100MB file claims to provide full Siri functionality on GSM or CDMA iPhone 4 units running iOS 5 or 5.0.1. However, this particular exploit seems like bad news for a number of reasons.

First, it’s illegal. The guys at iDownloadBlog were able to confirm this because the hack uses copyrighted binaries from the iPhone 4S.

Second, your Siri requests won’t go through Apple’s servers with this version of Siri — instead, they’ll go through the servers of the Chinese hacking team that developed the exploit. What’s more, CD-Dev Team, the group behind the hack, has confirmed that their servers are currently down, so even if you did download H1Siri, it may not work.

iDownloadBlog was not able to get the hack to work, but did hear from others who had gotten it to work “in short bursts.”

Doesn’t really seem worth the effort, if you ask Gadget Lab.

Hackers the world over are trying to bring Siri to iOS devices other than the iPhone 4S. They’ve had varied success, primarily stemming from the fact that Siri interacts with Apple’s own servers, and each bit of data that’s sent to those servers bears markers that identify the request as coming from an iPhone 4S. If your request doesn’t include that unique 4S identifier, you’re out of luck.

One of the most successful Siri hacking attempts thus far comes from a French team at Applidium, but the blog post detailing the hack seems to have been removed. Another hacker, Pete Lamonica, was able to use Applidium’s instructions to hack Siri to control a thermostat, while another developer then used Lamonica’s method to start and unlock his car. Both of the latter two cases still used an iPhone 4S, it must be noted, and simply hacked Siri’s capabilities, and not her host hardware.

Lamonica tweeted this morning that he would be investigating H1Siri, but didn’t recommend others interacting with a third-party-managed Siri server.

iPhone hacker Grant Paul also tweeted reservations about the hack. “Please note: if you use a proxy to access Siri, you may be sending your Email, SMS, Calendar, Contacts, Location, etc though that server,” Paul said.

Besides all that, jailbreaking itself isn’t necessarily a good idea.

Apple’s official statement from spokesperson Natalie Harrison on jailbreaking is thus:

“Apple’s goal has always been to insure that our customers have a great experience with their iPhone and we know that jailbreaking can severely degrade the experience. As we’ve said before, the vast majority of customers do not jailbreak their iPhones as this can violate the warranty and can cause the iPhone to become unstable and not work reliably.”

Apple provides more details on its stance regarding jailbreaking iOS devices in a 2010 post on Apple’s support forums. Apple says jailbreaking can lead to app and device instability, compromised security and a shortened battery life, among other things.

So proceed with caution if you must, but I think this hack is one best left to observing via YouTube.