How do I stop/disable unattended upgrades from being launched automatically?

I recently installed Trisquel 8.0 LTS (Flidas) on my Desktop PC which was running on Trisquel 7.0 for 4 year. The system became very slow. When I check the RAM and CPU Usage, I found that CPU is almost at 100 % I tun top to see what is going wrong and found that unattended-upgr is consuming whole CPU. I tried to kill it by PID using sudo kill 1803 but after sometime, it started again automatically. I know that Unattended Upgrades are purposed to install important security updates automatically, however I need to disable it being launched automatically. How do I do that?