Since upgrading to Windows 10, I thought I'd ask what I should be running. Under Windows 7, I had:

Avast
Comodo firewall
Malwarebytes (free version)
Spybot
SpywareBlaster

Is Windows 10 secure enough or should I start installing some new security software?

i have AVG internet security and the free version of malwarebytes on two win10 systems. no problems thus far ...

I've been using the Windows 10 built in software for years and have never had any issues with it.

I'm the same as John, I use Microsoft Defender on my private machines.

At work, we have Kaspersky, which is centrally manageable. Although I'm not happy with the new version, it has started issuing its own SSL certificates for all websites and essentially does a man-in-the-middle attack on all web traffic to be able to monitor it.

That means you can no longer look at a site's certificate, to see whether the site is legitimate or not.