(CNN) -- A well-known hacker on Sunday posted the first "jailbreak" for the iPhone 4.
The hack -- available at jailbreakme.com -- installs a program that lets iPhone 4 owners and others purchase apps from stores other than the Apple App Store.
To start the process, visit that website using the Safari browser on an iPhone, iPad or iPod Touch. Unlike other jailbreaks, this version reportedly can be installed from the Web, without the aid of another computer.
Hackers already had posted jailbreaks for previous iPhone models, but the jailbreakme.com site is the first jailbreak reported to work with Apple's newest model of smartphone, which went on sale June 24.
A blog called Dev-Team says a hacker named Comex contributed to the update. The news of the iPhone 4 jailbreak comes just days after the process of jailbreaking phones was ruled to be legal by the U.S. Library of Congress.
Before that ruling, the legal status of jailbreaking was murky. Jailbreaking an iPhone still can put you out of compliance with Apple's warranty.
After jailbreaking a phone, users can download apps that Apple has not approved for sale in its online App Store. Some of the more popular black-market apps include MyWi, which turns phones into mobile Wi-Fi hotspots, and IntelliScreen, which lets users put e-mail and calendars on their home screens.
There are rumors online that the iPhone 4 jailbreak could allow users to conduct video chats over 3G networks instead of just on Wi-Fi as the phone does now.
Once a phone has been jailbroken, another set of apps can be used to "unlock" an iPhone. Unlocked phones can be configured to work on wireless networks other than AT&T, which is the only official U.S. carrier for the iPhone.
In the U.S., unlocked iPhones will work on the T-Mobile network, but, because of technical differences, the phone will not work on Verizon or Sprint even if it has been jailbroken and unlocked.
The iPhone 4 hack was reportedly so popular Sunday night that jailbreakme.com was having trouble keeping up with the demand.
Other users complained that the hack unintentionally disables the iPhone 4's video chat capability and creates problems with multimedia text messages.
Comex, the hacker who says he's behind the new jailbreak, said on his Twitter feed early Monday that he is trying to work through those issues.
On the Dev-Team blog's post about the iPhone 4 jailbreak, some users complained about these apparent shortcomings.
Others seemed overcome with joy about the new hack.
"I LOVE YOU SOOO MUCH and i think I JUST CANNOT STAY HAPPY WITH SENDING A POST CARD FROM MY CITY!!!!!" one user wrote.
Apple, however, maintains that jailbreaking its products can diminish their performance.
"Apple's goal has always been to ensure that our customers have a great experience with their iPhone and we know that jailbreaking can severely degrade the experience," Apple wrote in an e-mail to CNN last week.