Less people use Linux than Windows meaning that less people are actively trying to hack Linux PCs so Linux is safer (one reason, but not the only why).
no, that is not the reason. there are enough people using Linux to create enough incentive for hackers to try their hands and they are doing it. the difference is that Linux is open source unlike windows, so when a security hole is found in Linux it is found fast and is fixed fast and the update is pushed to everyone to patch it fast.
in windows when a security hole is exploited by a hacker it will take time for Microsoft to find out what that security hole is, then it takes another time to fix it and push the update to everyone to patch it and most of the times it is not completely fixed.
- There will be a security problem with the use of Linux
i wouldn't call it "security problem" but if you are brand new to Linux then you will certainly have a lot of problems because you won't do what you are doing there. but it is not hard to learn the basics needed to use the OS you just have to spend some time doing it.