TORONTO - The second BlackBerry outage in less than a week disrupted service for millions of users on two continents yesterday, demonstrating how vital - and how addictive - the device dubbed the "CrackBerry" can be.

The company behind the service, Canada's Research in Motion Ltd., blamed a software upgrade for the problem, which it said was confined to North and South America.

RIM said that BlackBerry users were unable to send or receive e-mails and instant messages but did not lose phone service. Many users also found the Internet inaccessible. RIM said that the disruptions began about 1:45 p.m. (EST) on Tuesday, worsened about 6:30 p.m. and began to be fixed about 11:30 p.m. Service appeared restored by yesterday afternoon. RIM would not say exactly how many subscribers were affected.

The glitch comes after an outage last Thursday and at least three breakdowns in 2008. The latest problems are happening at an especially bad time for RIM, which is facing more competition in the market it helped pioneer.

"One of RIM's big advantages is that it's perceived as a reliable device," said Duncan Stewart, director of research and analysis at DSam Consulting. "To lose the advantage of reliability would be a very big deal for this company."

RIM has sold more than 75 million BlackBerrys since the gadget debuted 10 years ago.

It now counts 36 million subscribers around the globe and ranks second in the worldwide market for advanced "smart phones," with a 21 percent share, behind Nokia Corp.'s 39 percent, according to market research firm Gartner Inc.

BlackBerrys are especially popular in occupations heavily dependent on messaging - among lawyers and business executives, for instance.

RIM counts 500,000 subscribers in the U.S. government. President Obama is a BlackBerry devotee.

After originally focusing on corporate or government customers, RIM now gets most of its new subscribers in the consumer market, thanks to touch-screen models like the BlackBerry Storm.

But RIM faces innovative competitors such as Apple's iPhone, which had 17 percent of the smart-phone market in the Gartner report, and the new Motorola Droid. RIM's stock has dropped 23 percent since September.

The iPhone is beloved for its design cachet and the seemingly limitless supply of programs, known as "apps," that users can download to customize their phones.

BlackBerrys got apps later, and have fewer available.