Google Play Store hosts a variety of unverified apps which could steal your data even when a phone is locked.
Hackers uses a text message/SMS to sent you a link which may install a malicious app to hack you out of your phone.
A few USSD codes could save you to check whether your call,SMS,fax is being forwarded or not .
##002# – If your voice call or data call, or SMS call has been forwarded, dialling this USSD code will erase them.
*#21# – By dialling this USSD code, you would get to know if your calls have been diverted somewhere else or not.
*#62# – With this, you can know if any of your calls – voice, data, fax, SMS etc, has been forwarded or diverted without your knowledge.