Every android device offers you a security option. Based on the model variety , password options can be accessed. Mainly they can be accessed by .Open settings-Security-Screen security.
Most secure option is to set a password considering the unavailability of FINGER PRINT lock. It is the most secure option followed by PASSWORD, PIN and PATTERN LOCK.
If you have already set a password for your device you can encrypt your device under SECURITY settings. Encryption can help to protect all of the data on your smartphone. This means that you have to enter the password on startup. It is a one way process in most Android devices.
Google has provided android with an app store free from malicious apps.Using pirated apps can expose your device with malicious code injected to these apps. It is always better to keep out from these places.
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know your permissions
Know your app permissions
Android smartphones running Marshmallow have greater control than ever to manage these permissions. While it would be unreasonable to expect users to micro manage all of their apps all of the time, you can use this function to keep on some key permissions that pose the greatest risks.
Android is well known for its seemingly never-ending customization options. Root is not for everyone, as the risks can far outweigh the benefits and you are likely to regret your decision once things get messy.It voids your warranty, brick your phone. Rooting makes your device more vulnerable to threats. If you have enough knowledge on rooting you may continue. Always know while rooting you are making changes to your stock operating system.
There are many free antivirus apps available on playstore. Use these to protect against threats.there are also some additional options provided by these aps such as app locker etc.
Another way to secure your device is by installing ANDROID DEVICE MANAGER developed by Google. It helps to secure our lost device. It also provides options like Lock, Locate, Ring your device if it is lost. User must provide permission to activate it as administrator.
Always manage to backup your data. If your phone met with some problems and lost all the data this backup could really help you. There are apps to back up your data. Even you can store these data online or flash to a drive.