One of Androids big issues is with being an open source OS that 80% of the world uses is that it is a HUGE target for malware and spyware. Windows for computers had this issue for years and Microsoft had to be on top patches and updates so it's user felt safe. Google is in the same spot right now and it looks like they are pro active and doing something about it. Well at least in their own report they released on Android Security last year.
According to the report:
The percentage of devices with PHA (potentially harmful applications) are on only .1% of devices that are not rooted. That is an extremely low percentage on any OS. Even with sideloading the number of affected devices remains pretty low. Check out the graph below the shows affected devices broken down by country:
Even the sideload apps are getting safer according to Google:
"The worldwide average rate of PHA installs outside of Google Play has decreased by 50% between Q1 and Q4 of 2014"
This report had much more to offer than the few highlights I showed you it's worth reading for yourself and you can check it the full report here.