It's important to note which things are theoretically hard vs lack of tooling. Using a VPN after Tor might defeat a bad exit node sniffing or changing content.

It's important to note which things are theoretically hard vs lack of tooling. Using a VPN after Tor might defeat a bad exit node sniffing or changing content. But a VPN absolutely hurts anonymity. Plus there's no way to be sure the VPN op isn't keeping logs. If I were at the NSA and concerned about any of this, I'd start a few VPN companies. And run Bitcoin exchangers/vendors.