Skype for Android app has a serious bug which was discovered by a Reddit user recently. This bug allows someone to spy Skype for Android users. This is how it works,
1) Have 2 devices signed into your skype account. Desktop and phone will do.
2) Call the target’s android skype account with device 1.
3) Disconnect device 1 from it’s net connection as the target phone is ringing.
4) Target phone will immediately call you back.
5) Pick up with device 2.
Thankfully, Microsoft is working on a fix already. For now, you just need to sign-out of Skype app on your Android device to protect yourself from others.