Like many teenagers, Ari Weinstein spends his summers riding his bike and swimming.
This year, the 15-year-old had another item on his to-do list: Foil Apple Inc.'s brightest engineers and annoy chief executive Steve Jobs.
Ari is part of a loose-knit group of hackers that has made it a mission to "jailbreak" Apple's iPhone and iPod touch. The term refers to installing unapproved software that lets people download a range of programs, including those not sanctioned by Apple.
Since Apple began selling its latest iPhone 3GS on June 19, Ari and six online cohorts spent hours a day probing the new product for security holes
This weekend, one of the members of the group, dubbed the Chronic Dev Team, released the jailbreaking software they've been working on.
Ari says the program is a test version with some bugs, but that users have successfully downloaded it. A quarter-million people have visited the site, he says.
"Coding and testing things that may or may not work, and figuring things out, is a really rewarding experience," says Ari, a Philadelphia resident who began hacking when he was 11.
Ari's hobby has ruffled the feathers of famously secretive Apple, which exerts tight control over its gadgets and sells programs for its iPhones exclusively through its App Store site.
"The vast majority of customers do not jailbreak their iPhones, and for good reason," an Apple spokeswoman says. "These modifications not only violate the warranty, they also cause the iPhone to become unstable and not work reliably."