There really is no tweak to protect yourself from any type of attack you mention; most of what you can do is user-generated. The biggest tip is, if you are on public networks, use HTTPS and VPN protected browsing and stay away from servers you don't trust or that seem "hinky." In addition, make sure your home WiFi is secure behind a password (with WPA encryption).
As a side note, I'm assuming you have SHSH blobs for the iOS 4 version you want to go to? Because no blobs = no downgrade...
Regardless, I hope this helps.