Can Kindle Fire HD devices get viruses from the Internet?

So I do visit some sketchy websites on my kindle fire hd (4th generation) and I frequently get pop ups. (My friend told me that you can't get viruses on a mobile device.) I usually just hit "OK" and x out of the pop up as quick as possible, before doing whatever I planned on doing on said websites. I've done this for around a year and I have had little problems here and there. My volume will increase and decrease on it's own occasionally. It will go into sleep mode on it's own (While I'm using it, I could be tapping it and actively using the device and it'll do this.). On some occasions, it restarts on its own. So does my kindle have a virus? And if so, how can I remove it?

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