I have made an account, still though is there any malware or hack which can lock mobile phones on general?
Nothing commonly known. Ransomware is always a potential threat, but that has been limited to Windows PC thus far.
If you're concerned about malware, then here is my spiel about it:
For the most part, it's still quite difficult to get an actual virus on your phone, because malware requires you to manually accept the installation (which is why they try to fool you into thinking you're installing something legitimate). Use common sense:
1. Avoid shady websites that deal with things like porn, gambling, and "free" (aka pirated) apps/music/movies.
2. Never tap on a link that appears in a popup while browsing, especially if they're warning you that your phone is infected -- they're just trying to scare you into installing some bogus "antivirus" app that is probably malicious itself.
3. Only install apps from well-established app sources like Google Play Store or Amazon Appstore. Read a bunch of app reviews before installing an app to look for any complaints about adware or suspected malware.
4. Turn on Google Play Protect features in
Settings>Google>Security (or in the Play Store settings). This allows Google to periodically scan your phone's apps to look for malware.
5. Turn off "Unknown Sources" in
Settings>Security (or in Special App Access on newer phones). This prevents any app that wasn't obtained from Google Play Store from being installed (which could include malicious apps that are inadvertently downloaded).