How to fix badly virused android device - Your device has been modified, software updates are not available
It sounds like you have it unlocked with a custom recovery. If so, use the custom recovery to install a new ROM for your tablet. Find your tablet on http://forum.xda-developers.com/ and you can find either a third-party (i.e. Cyanogenmod, etc.), modified stock, or even completely stock ROM such as this one: http://forum.xda-developers.com/showthread.php?t=2792979 .

If you don't have a custom recovery, you can find instructions on XDA to use the odin utility to install one. 

Wiping the system and data partitions should get rid of the malware but you'll need a new rom to install. If you have an SD card you can put the new rom zip file on the card. If not, you should copy it to the tablet first.