How to tell

Solution
Install an anti-virus app run it. Is the phone doing something strange like redirecting web pages or flashing screens a lot when you use apps, especially those that need a password like your bank app? If you are worried the phone is compromised, you can factory reset it and it will wipe everything off the phone and set it up like it was new. Just make sure you have backups of what you need off the phone and remember your account info on whatever you installed on it.
Install an anti-virus app run it. Is the phone doing something strange like redirecting web pages or flashing screens a lot when you use apps, especially those that need a password like your bank app? If you are worried the phone is compromised, you can factory reset it and it will wipe everything off the phone and set it up like it was new. Just make sure you have backups of what you need off the phone and remember your account info on whatever you installed on it.
 
Solution