SAN FRANCISCO -- RSA Conference 2010 -- A pair of researchers has amassed nearly 8,000 iPhones and Android smartphones in an experimental mobile botnet project that demonstrates the ease of spreading potentially malicious applications on these devices.

Derek Brown and Daniel Tijerina, security researchers with TippingPoint's Digital Vaccine Group, demonstrated how their seemingly innocuous weather app -- called WeatherFist -- gathers information on the users who downloaded it, including their GPS coordinates and phone numbers.

The researchers wrote the app, which links to the Weather Underground Website and provides local and other weather forecast information to its users, and submitted it to app clearinghouses that offer apps for Androids and jailbroken iPhones. "We could get into the jailbroken [iPhone] market and deliver our app," Brown says.

They decided against Apple's iPhone AppStore as a way to distribute their app because apps undergo fairly rigorous vetting there: Code must be digitally signed by Apple, and apps can't "phone home" or contain private APIs, for instance. And approved iPhone apps run in a "sandbox," which prevents them from gathering data from a phone they aren't authorized to access.

The Android's official app marketplace was a bit too restrictive, as well, although their app doesn't require a jailbroken Android. The researchers used other online app stores that catered to jailbroken iPhones and other smartphones. "We wanted people to feel comfortable using the application and putting it on their phone so we would have permission to do a lot of things like pass GPS coordinates, write to the file system, and surf," Brown says.

A Google spokesperson reiterated that the app was not distributed via the Android Market. "Any user trying to download this application would need to change a setting on their Android device and bypass a security warning screen to enable downloading applications from other Websites," the spokesperson says. "Additionally, the Android application sandbox and permissions model requires a user to approve a list of permissions specified by applications before downloading. For example, a user must explicitly approve an application to access resources like location or the address book."

Within an hour of the app being set up on the SlideME and ModMyI app sites, the researchers had 126 downloads, and 702 after eight hours. "After 24 hours, we had 1,862," Tijerina says. And as of yesterday, the count was 7,800 iPhones and Androids running the app. "This was really surprising because if this was malicious code, that's a lot of bots we would control," he adds.

WeatherFist basically sends a request to pull the user's GPS coordinates and then sends that data to a server, where it's converted into the user's ZIP code. The ZIP code is passed to the Weather Underground site, which loads up the local weather information and forecast.

To prove the dangers of a mobile botnet, the researchers also wrote a malicious version of WeatherFist, called WeatherFistBadMonkey, that appears to the user as WeatherFist, but is really running bot code and can grab contact information, cookies, and physical addresses, and can send spam runs. They have run this app only on their own phones, not on those of their WeatherFist users.

The researchers have no plans to release WeatherFistBadMonkey due to its potential for abuse. "Nobody else is going to get this app," Tijerina says.

So why the WeatherFist experiment? The researchers say it's to prove how such an app could steal or modify a user's contacts, read his files, and access his Facebook and Twitter accounts, as well as email and passwords. "We could enable or disable system services [with a malicious app]," Brown says.

Brown says he and Tijera toyed with the idea of alerting WeatherFist users about the purpose of the app. "We considered sending messages to the users of our app and telling them to come see our talk here, but we didn't want to self-promote," which isn't the goal of the research, he says.

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