To use apt-get to install a specific (perhaps older) version of a package, follow the package name with an equals sign and the exact version number. For example:

# apt-get install bash=3.0-17

If you need to move files, logs, or any kind of program output off a compromised system without disrupting evidentiary data on the disk, use netcat.

On your trusted system:

$ nc -v -l -p 2222 > victim.dump

On the victim's system:

$ <program> | nc <trusted_system> 2222

Where program is the discovery application you're running (e.g. netstat -an).