In the latest example of the dicey line between the virtual world and the real one, Apple Inc. yesterday apologized for selling Baby Shaker, an iPhone application that let users silence an imaginary crying infant by shaking the multimedia device.

The 99-cent "app" was removed from Apple's online store on Wednesday, two days after it debuted (although it endures on YouTube). Outraged child-welfare groups that decried it as "horrifying" and "reckless" demanded an apology - which they finally got.

Apple spokeswoman Natalie Kerris said in a statement that the software was "deeply offensive" and should not have been approved for sale.

Searching for a silver lining, pediatrician Cindy Christian, co-director of the Center for Child Protection and Health at Children's Hospital of Philadelphia, thanked Apple for finding "an unfortunate way to raise awareness" of child abuse.

"Unfortunately, more than 1,000 babies die each year from being shaken and countless more are left with permanent brain damage," she said. "I'll use any way we can get the message out: It's not OK to take your frustrations out on a crying baby."

Apple on Wednesday posted a 15 percent increase in quarterly profit, largely thanks to its booming iPhone business. The iPhone app store, launched less than a year ago, has sold nearly a billion (maybe more by now) of the low-cost downloads. Both established and wannabe software developers provide the applications in hope of fortune, maybe even fame.

Apple and the developers share the proceeds.

Until now, Apple's process for vetting those tens of thousands of submissions - games, restaurant finders, dictionaries, you name it - has kept controversy at bay. Apps such as iBeer, which is basically a sight gag, and iFart, which is just what it sounds like, may be sophomoric, but they're not horrifying.

The app store "has a lot of what I'd call throwaways," said Christopher Swain, a game designer and professor at the University of Southern California School of Cinematic Arts.

One such app that Apple allowed and then yanked was called IAmRich.

"It cost $1,000," Swain said. "Apple removed it because it thought the developer was abusing their network. But eight of them sold. . . . And now the eight people who have it, it's this notorious thing, so it's even cooler."

Baby Shaker was not cool.

"I think [Apple] probably made a judgment quickly that this was playful or whatever," Swain said. "I think it's terrible."

Similar controversies have blindsided other nascent, novel interactive technologies, Swain said, because their popularity grows faster than the ability to control them. YouTube has been accused of copyright violations and video piracy, at one extreme, and censorship at the other. Downloadable games such as Grand Theft Auto have been criticized for glorifying illegal acts.

And Spore, an interactive online video game in which users create "creatures," had to install a rating and filtering system because of the proliferation of offensive content.

"It's so easy to make these animated creatures that some users started making pornographic creatures," Swain said. "They call it sporn."

As apps go, Baby Shaker is low-tech and low-brow. The developer, called Sikalosoft, described it this way: "On a plane, on the bus, in a theater. Babies . . . are always distracting you... with their incessant crying. Before Baby Shaker, there was nothing you could do about it."

Sketches of a cherubic infant appear on the iPhone screen and the sound of crying is heard until the phone is shaken - turning the baby's eyes into blood-red Xs.

Coincidentally, the American Academy of Pediatrics on Monday will issue an updated policy statement, coauthored by Cindy Christian of Children's Hospital, urging doctors to abandon the well-known "shaken baby syndrome" terminology in favor of "abusive head trauma."

The change, Christian explained, reflects the fact that injury is often a combination of shaking, beating and throwing an infant.

"Shaking is a very important mechanism, but not the only mechanism," she said. "To call all of it 'shaken baby syndrome' is not accurate. A lot of these cases go to court, where mechanisms need to be accurate."

"This area is really quite controversial," she added. "There is a small group of professionals who don't believe you can do harm by shaking a baby."