Google’s Android smartphone operating system uses source code contributed by the US National Security Agency.
Especially in the post-Edward Snowden era, that’s a red flag for
Beijing, and helps to explains why China has been so eager to encourage
the growth of non-Android smartphones within its borders.

Security Enhancements for Android is one of several projects
that the US spy agency contributes to open-source operating platforms.
Ostensibly, the NSA’s addition to Android is designed "to raise the bar
in the security of commodity mobile devices,” an NSA researcher told Bloomberg Businessweek. And indeed, anti-hacking protection is actually what the spy organization is supposed to be providing.

But you can bet that Beijing is dubious about the NSA’s stated aims, especially after news that the US agency hacked millions of Chinese SMS messages and is working closely with American technology firms. Even before Snowden’s leaks, China was directing stinging criticism
towards Google and Android—used in at least three quarters of China’s
mobile handsets—and accusing it of "commercial discrimination” against
Chinese companies. Apart from security concerns, Beijing is also keen to
promote its own fast-growing tech companies, some of which are chafing at Google’s dominance.

http://qz.com/102346/no-wonder-china-is-worried-about-android-the-nsa-helped-write-its-source-code/