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If you're visiting YouTube without adblocker or an extension like Ghostery that removes tracking, chances are well your data is being tracked(which usually happens) or your PC is being used for mining. Yes visit a site and you'll spot within your Task Manager that CPU usage is going up while you're doing nothing not even running the video from the site.
This issue first came to light when user's antivirus spotted malware coding from accessing the site, the leechers apparently have hacked into Google's DoubleClick to mining Monero which gets better yields from both CPU and GPU.
YouTube now joins a list of other sites that spread malicious coding around people's computers, especially with Anti-viruses that scam people into downloading them.