I recommend that you install Kaspersky (free or paid), I was with this same problem, when I bought (at the beginning of the year), the 2018 version was lighter for me, but then came "Bitdefender Total Security 2019", weighed even more, so for those who had weak PC (like me) do not recommend install. Bitdefender is good, yes !! , but for a person who has:
- Processor: Intel (R) Celeron (R) N2820 CPU at 2.13 GHz 2.13 GHz
- Internal memory (RAM): 4.00 GB (usable: 3.98 GB)
ends up being complicated, until it gave rise to the problem "100% HD" in my notebook !!