In the beginning there was Linux and it was virus free. Then came the windows PC and it had all the viruses anyone ever wanted...

Joking a side it used to be that only Windows PC's used to get viruses and computers running Linux (variations) or Mac OS boasted that their systems couldn't be infected. Over the years this has been proven to be wrong and nearly all computers have some form of firewall/virus protection.

Now it seems that the inevitable jump to mobiles is happening.

How can you keep your phone safe?

Download only applications (as well as files) that are from trusted suppliers. The Play store is vetted a lot but they can't catch everything. Another option is to try anti-virus software specifically made for mobiles. I recommend Avast Free Mobile Security.