Somewhat OT, but related...
I am sure most everyone here that has a PC also uses a good Anti-virus software utility that is on your PC.
If you want to scare yourself, open up your main Antivirus Application Menu., and there is usually a place you can see "Reports" or "History" of any activity that the utility has removed or deleted for you.
Its usually in the Firewall OR Internet Security areas.
When finding these reports and/or activity, you will usually be amazed at how often your PC was "attacked" by malicious files, tracking cookies, etc.
My Norton gives a monthly report of such activity and I find stuff it catches at least once a month. Its very scary stuff and which is why it is so important to have a good trustworthy antivirus software running all the time and be updated.
The "signature files" are lists of known malware that are updated regularly by the antivirus software companies because they keep track of all the known attacks and add them to the signature files. The software uses these files to recognize known bad files and bad website links to prevent your PC or device from going there or downloading it to your PC.