Malware aimed at Android mobile devices jumped a whopping 76 percent in just three months, found a new report. That makes the operating system developed by the Google-led consortium the most attacked mobile operating system by a landslide.

Security firm McAfee's second quarter 2011 threats report counted 44 new Android-specific malware attacks, which put the operating system in first place. Far behind, in second, was J2ME (Java Micro Edition), with 14. Symbian (Nokia) and BlackBerry each had four.

Part of the problem, of course, is Android's popularity—which makes it more appealing to hackers. Android captured 61 percent of ad impressions on the mobile ad network in July, according to a separate report from advertising firm Millennial Media. This was the eighth consecutive month it was in the lead. (Last month, Apple sank to 21 percent of impression from 26 percent in June.)

The Millennial report also charted mobile developer trends by ad spend: Android represents 48 percent of the platform mix, to Apple's 43 percent.

David Marcus, McAfee Labs' director of security research, told The New York Times that Android users had become the top target because Google does not vet the distribution of new mobile apps. Anyone can post an app on the Google Apps Marketplace—and that includes hackers, who tuck their malware inside free mobile software and games. Apple, of course, must approve each app that appears in the iTunes store.

One other tidbit from the report: The U.S. is a relative bargain for spammers. The going rate for 1 million U.S. e-mail addresses is $25. That's compared to $66.66 for the same number of U.K. addresses and $166.66 for 1 million Portuguese. Twenty-five dollars also buys hackers a million German, Russian, or Australian addresses. The Ukraine was the cheapest, with a going rate of $20.