I can't find any useful information about this in Google, so it is difficult to track this down.
I would start scanning. I assume this is a Windows PC, but am not sure what version of Windows you are using. However I would download and install the two free anti-malware utilities listed below;
Malwarebytes' Anti-malware, and SUPERAntiSpyware.
Then one at a time, open each utility and update it's definitions, then run a full scan with each.
These free versions are 'manual' scanners. Your own Anti-Virus scanner still runs in the background, but these two utilities can just be used to carry out double check scans once a week or so. SUPERAntiSpyware may set itself to run at Startup, but you can change that in it's Preferences.
See how you get on with those.
I think Skype (or a Skype user) has hacked my PC. It has slowed down to impossible slowness, and shows a nearly unbroken 100% usage under Task Mgr. When I shut it down, I see a message box "End Program - SKYPE CALLBA...". I never installed Skype; my adult son swears he did not do so (and I believe him). I have to set my ZA firewall to "Stop all Internet Activity" to use my programs. Open the firewall to check my email, then lock it again. This has worked for the last few days or so - but why the closing message box?? Oh, yes - in the registry, I found 2 lines for 'BRSkype Plugin.DLL'. I didn't touch them, because I don't remember the filename of the registry; and don't remember how to disable a line without deleting it. (Old retired programmer / network person here....) Skype is not listed in the REMOVE PRGM portion of the Control Panel. How do I get rid of this unwanted invader? Is my PC a zombie for some hacker out there???