because i do not. just windows defender and malwarebytes.

Just make sure nobody puts any unauthorised floppy disks into your computer and you'll be fine

You're aware Windows Defender is an anti-virus program, no?

I have been running for a long time without AV, until my kids starting using the machine.
So yeah, why not, if you know what you are doing. It will make your computer notably faster.

I'm not sure I believe bit defender noticeably slows down a modern computer

Hello! It's okay to not install other AVPs. Windows Defender is already a reliable one.

thank you good sir!

https://www.av-test.org/en/antivirus/home-windows/

I mean, windows defender is simply bad at detecting threats.

I stopped using anything, but my Windows desktop is 50% work computer and 50% home recording studio, so no real surfing or casual web use. I generally use my MBP for that, or checking my bank account or buying anything

I agree but over the years I am using it I found it reliable enough.

It's good that that's been your experience, but it's simply not a true statement that it's good at detecting threats.

Same ,and also installed spyware blaster ,but I don't know why .. So what can be best solution for rootkits ?

As pointed out above, Windows Defender has a less than stellar reputation.

A good starting point with free software to secure your machine would be Malwarebytes (used regularly for on-demand scanning) plus one of the better free always-on AV products out there, like the free editions of Bitdefender, Avast, or Avira.

I'm not sure how well regarded Spyware Blaster is these days (but in any event it's another on-demand service like MBAM and is not a substitute for a proper AV product).

Do you use an administrator account or one with limited rights for your day to day use of Windows? Getting that right will probably give you a far better starting point that installing lots of things like Spyware Blaster.