How do I remove/check for viruses?
If you're on Windows, I would recommend you download HitmanPro to do a quick scan to see if you have anything malicious on your device.
The free version won't let you remove the malicious files, but it at least tells you that actions are needed.
Malwarebytes can scan and remove malicious files from your Windows computer or Android device as well. Real time protection requires premium for both Windows and Android.
WiseVector StopX is currently free and offers everything in one. Full real time protection (really effective). This program will NOT remain free (as they told me) though so enjoy it while you can. It is also worth mentioning that this is a Chinese program. This program will work without internet access (firewall) and you can update the database whenever if you don't trust it.
UVK (Ultra Virus Killer) is a hidden gem program that lets you scan your computer for malicious files, processes, etc. and remove them. Be careful when using Threat Scanner as it tends to auto select things you might not want deleted such as browser bookmarks or extensions.
If you're on iOS you might as well just give up as there are no anti-virus apps. Its unlikely you would have something malicious anyways, but not impossible.