Can My iMac and iPhone be hacked into from someone else using there own iPhone without my knowledge?

Can My iMac and iPhone be hacked into from someone else using there own iPhone without my knowledge?

The only answer that would be correct is maybe, it's definitely possible if you downloaded an app or program that has spyware in it or if you visit an infected website that has a virus, trojan or spyware on it for someone to hack your system or access all your data and passwords using a keylogger and that's why we have to buy and use antivirus software on all our devices, even phones and tablets if they have internet access and we install any programs on them or use a web browser

  • What should I do if someone hacked into my Apple ID? Last night, someone went into my Apple ID. This person sent a plenty of abusive messages to my contacts. I know I didn't do it, because I was just busy watching videos while that person was sending messages. So I have blocked all my contacts to keep low from this person. Well I used to a iPod touch and I lost it last year in my school. After when I lost it, someone must have found it and went inside that account. So is there anyway I can do? I own a iPhone 6S btw
  • Using someone else's Wi-Fi on iphone, can they still see your app history? Yesterday I went to work with my friend and I used the places' Wi-Fi, I'm at home right now and no longer using their Wi-Fi, can they track my history and app history in my iphone even if I'm not using their Wi-Fi anymore?
  • Is there a way I can use an iPhone that's logged onto someone else's iCloud? I recently found an iPhone 5s out in the street perfectly fine but it's logged into the owners iCloud and in order for me to restart it I have to put in that persons password and I've been told that there's no way for me remove that account. So I was wondering if anyone knows if it's safe to use it like that and just add another account or if I can use it some other way?
  • How to clear someone someone else's iCloud info off my Iphone 5? I got a used iPhone but the previous owner didn't wipe the phone and it still has all of his data on it. When I try to log off his iCloud or reset the phone it asks for his iCloud password. Is there a way to do this without his password? It's my brother's boss's old phone so I feel a little weird asking for his password.