Q: iCloud security

Hey guys. I'm a fairly seasoned Mac user. Since the late 80's. In fact the Mac is all I've ever really used. But I'm new to using the whole iCloud backups and storing data and other files there. How secure is it? With people hacking things every tie you turn around these days, I'm just concerned about my data being out there for someone to possibly hijack. Could someone give me the story on security with iCloud and whether you feel safe keeping your data there? Thanks