Punit Soni, the lead product manager of Google+ Mobile, told Slashgear.com he discovered early in the day that an old test version had been posted and announced it on Google+ immediately.
But because the app was so popular, thousands of users downloaded the incorrect version, he said. The system fixed itself and was providing the right version within 2 hours.
The number of the correct version, visible above the help button, is 126.96.36.1999. Users with a different number are advised to uninstall and reinstall the app.
The Apple version of the social networking system is similar to the Android model, sharing key features like the Stream, Circles and Huddles, the Los Angeles Times reports.
The chief executive of another networking site, LinkedIn, meanwhile, wonders where people will find the free time to use the new service.
"Nobody has any free time," Jeff Weiner said at the Churchill Club, a tech industry forum in San Jose, Calif. "Unlike social platforms and TV, which can coexist, you don't see people using Twitter while they're using Facebook, or using Facebook while they're using LinkedIn."