So... Windows Defender caused my Memory and Hard Drive usage to go up to 100%

I was working on a reddit text post (while downloading Grand Theft Auto 5) and decided to switch tabs on Chrome when the computer froze up... It was working but only 0.01% of the time, the apps wouldn't respond, nothing would load and it felt like I was at a loss as to what would be causing this.

I did open Task Manager and found out Windows Defender was the culprit.

It used up all 16GBs of RAM as well as accessed my hard disk thus making my computer completely unusable. Since Microsoft doesn't allow the option to end the Windows Defender antivirus service (which is stupid since I did it before) and since I couldn't get the Windows Defender app to load; I had to hard reboot the computer.

No real damage was done but the reason I'm making the post is to make people aware of this. I don't know if it's a bug that causes Windows Defender to use up all available resources making the computer unusable or if there's an exploit that can be used to wreck real havoc to computers; I downloaded a game from Steam before and this has never happened but now it has happened...

I have disabled real-time virus protection and left the firewall on in the meantime. I'm browsing the web unprotected but unless somebody has any info on why this is happening, I'm afraid to turn real-time protection back on.

I don't know if there's a free AV that's as good or better than defender and I don't know if switching to an SSD or adding more RAM will help; especially considering it used up all the RAM and made my HDD crazy. For now, I'm taking a risk until I get more info or a solution.