In less than two months, the free Pokémon Go game for iOS and Android phones or tablets has zoomed to global popularity as one of the most-used mobile apps. It reportedly has been downloaded by more than 100 million people worldwide since early July and has generated more than $200 million from in-game sales of upgrades to speed play and add features. Players use their mobile device's GPS capability to find, capture, battle and train animated Pokémon creatures who appear on the screen as if they're in the same real-world location as the user. In North America, 142 "pocket monsters" are in play. "Gotta catch 'em all," a promotional slogan says.

Players are easy to spot by their concentration on handheld devices, walk-and-stop pace and swipes on screens. Pokémon Go is credited with popularizing location-based and augmented reality gaming, as well as for promoting physical activity. On the downside, it stirs controversy for contributing to accidents by inattentive players and for being used inappropriately at cemeteries, memorials and museums. Israel bans the game from Army bases, while Kuwait prohibits playing at any government sites. Iran, citing security concerns, goes furthest by prohibiting Pokémon Go downloads or use.

The game's popularity follows the spread of computer-generated imagery in movies and TV shows. Computer science advances could give players an even more realistic experience in coming years. A new imaging technique could help make imaginary characters, such as Pokémon, seem to interact convincingly with real objects.

Developer says: "We have been working crazy hours to keep the game running as we continue to launch globally." – Niantic post on Facebook, Aug. 2

Player says: "I've yet to catch 'em all, and I', not sure I ever will, but I'm close [141 out of 142]. . . . The hunt must go on.” – Brad Flora, San Francisco tech executive

Critic says: "Unstructured outside play is one of the best ways for children’s brains to recover from school pressures and excessive screen media. Inventing games, building forts or just playing a pick-up game of soccer are all ways to increase their imagination, creativity, social skills and critical thinking." – Kristen Race, family psychologist in Steamboat Springs, Colo.