It's a fact that Android is less secure than Apple's iOS overall. One reason is because manufacturers can add their own apps and changes to Android that might have security problems. Plus, Android gives users more freedom to install potentially malicious apps and change low-level settings.
Since Google released Android, it's been steadily working to fix some of the biggest contributors to poor security, from scanning for malicious apps in the Google Play app store to monthly security updates. Unfortunately, your gadget might not receive some of these updates.
If a manufacturer or carrier wants to push out an updated version of Android, it has to test it first to make sure the patch didn't break anything not in the original Android. It also needs to test the update on every gadget it makes just in case there are hardware glitches.
That takes time, energy and money. It's why security patches can take weeks or months to appear, if ever. Samsung and LG signed on to Google's monthly updates, so owners of their gadgets should have updates at some point, but many smaller manufacturers haven't.
Of course, there's also a question of which version of Android you're running. Most manufacturers and carriers don't upgrade older gadgets to the newest version of Android. It goes back to the time and money it takes to test a modified version of Android on older hardware. Why do that when you can just sell new hardware with the new software?
You could easily still have a gadget running Android 4.4 or earlier (the latest version is 6.0). And your older version of Android is probably not going to get any security updates.
Now you can find out where your gadget stands with the free VTS for Android. It scans for 22 of the biggest security flaws, including several versions of Stagefright. Just note that if you're running some security apps, it might trigger a false positive for a malicious app because of the way it scans.
If you do have security flaws, check with your manufacturer to see when updates are coming, or if they are. You should also make sure you've taken good security precautions to make your gadget as hacker-proof as possible.