Awhile ago I created a Ubuntu 11.04 USB Flash drive (with persistence) which I would occasionally boot to on normally windows 7 machines. I forgot all about it and recently found it again and decided to play around. After booting into the flash drive, I got a message about being out date and upgrading to latest Ubuntu if I want any further updates.

Question 1.....can I upgrade Ubuntu on a USB flash drive the same way I would if it was installed or do I have to just erase the drive and reinstall the latest version of "live" or whatever it is called?

Question 2....more generally....when I run Ubuntu from the flash drive, can I assume that the windows hard drive is completely isolated from anything that happens while running Ubuntu? No malware can migrate to or from? I am not running it on top of windows...but rather using the boot menu to go directly to the flash when starting up.

Thanks