I recently heard that virus program distributed among the android users and they encrypt their data and ask money(Through a wallet address) for recover them
Do you mean ransomware? But i never see it on android before.
the thing is transaction cannot be tracked? why?
Well, for me is possible to track it but its really hard, especially if the hacker(people who ask money) using mixer before send it to exchange. If the hacker send it directly to exchange address without using mixer, then it probably still have a chance to track it, cmiiw.