Step 1: Securing /tmp
Step 1.1: Backup your fstab file

Step 1.2: Creating tmpmnt partition file (Around 1Gb in size)

Step 1.3: Format the new partition

Press Y when asked
Step 1.4: Making backup of old /tmp

Step 1.5: Mount the tmp filesystem

Step 1.6: Set the right permissions

Step 1.7: Copy the files back to new tmp folder

Step 1.8: Adding new /tmp filesystem to fstab

Step 2: No need for 2 tmp filesystems, so we symlink /var/tmp to /tmp

source: http://www.directadmin.com/forum/showthread.php?t=29807&page=1