How dangerous is jail breaking for two things?

[Mjmar]

I only want to use mywi for tethering and backgrounder. Since these are trusted sources isn't there no way for me to get a virus on my iPhone? I'm being paranoid.

 

[Doju]

Definitely not. They're basically like App Store apps that Apple wouldn't want to approve. No security flaws to them.

 

[Penguissimo]

Yeah, these are widely-enough used apps that we'd probably have heard by now if they were a virus. If you're worried, just stick to stuff from the default repositories and you'll be fine.

 

[Applejuiced]

Exactly.
You will be fine with Backgrounder and Mywi.
Both my favorite JB packages.