it is safer to store your coins on a hardware wallet:
https://bitcointalksearch.org/topic/overview-bitcoin-hardware-wallets-secure-your-coins-899253
it is, but sometimes you need to pay for something online, you need to copy the addresses, it might be easier to check and find the flaw, but it is still a risk that the address sending too is changed when copy-pasted.
Thanks for the warning, do scan my devices regularly, not just for the bitcoin, better safe than sorry.