1. Yes, unfortunately. The issues began the day I installed Kaspersky Premium and have continued since, regardless of whether I uninstall Kaspersky or keep it on. When I say "nothing is working," I primarily mean internet access via a few apps and websites through Chrome/Firefox.
2. Did Kaspersky support say whose responsibility it was? Yes, they want Apple to investigate first, as the issue persists even if Kaspersky is uninstalled. It's not unreasonable, but I strongly feel it's coming from Kaspersky, as the problems started the day I installed it.
3. When investigating, did Kaspersky support request any logs, traces, or other data? No, they want Apple to investigate first.
4. INC000016459246
5. Has User1 been deleted and recreated? No, that's my main account where I keep a lot of files, and I did not want to experiment with it. Should I try that?
6. I've done it. I think it affected some behavior. Namely, I can access some websites, such as amazon.com, but still cannot access others like gmail.com or dropbox.com.
Any help or hints on where to look for a fix would be greatly appreciated. Currently, it's very hard to use my computer.