that depends on how many clients you have and how many revisions you have set for the virus defs

to clear the space

open admin

servers

local site

right click properites under liveupdate

revision will be 30; make it ten;

or 

clear all the corrup defs using this document

http://www.symantec.com/connect/articles/how-clear-corrupt-virus-definitions-sepm

I had this issue recently, albeit with 11.0.5 RU5.  We used to keep 3 days of defs but now keep thirty days as our links to remote sites were getting hammered.  I found that there was older content than thirty days under the GUID folders in C:\program files\symantec\symantec endpoint protection manager\Inetpub\content\.  I stopped the SEPM service and deleted all the numbered folders over thirty days old. NOT the GUID folders ones like {C60DC234-65F9-4674-94AE-62158EFCA433}, but the ones inside those folders.  I restarted the SEPM service and it has been working since, clearing out content over 30 days without intervention.  Maybe this will sort your issue out without having to do all the other stuff in the article. HTH.

If you change the number of revisions kept, this should save on some disk space.