How to backup files without destroying the destination?!

[ml]

Hello List,

i would like to copy/mirror/rsync the backup files from ServerA to ServerB.
Since i must assume that ServerA is hacked (public server with a few 
services), i would like to "pull" the files to ServerB (save server with 
no services).

That means i do something like: rsync -avz ServerA:/backup ServerB:/backup

IF ServerA gets hacked and the files get zeroed out (every file has 
rubbish or 0 bytes), then i would also destroy my files on my 
destination ServerB.

Whats a good way to prevent this?
Any ideas are welcome :)

Cheers,
Mario