Also, keep in mind the below:
"If you update a Defense Center from Version 5.4.1.8, the system re-installs all intrusion rule updates instead of the latest intrusion rule update and the update takes much longer than the projected time listed in the Time and Disk Space Requirements for Updating to Version 5.4.1.8. To reduce update time, Cisco strongly recommends updating to Version 5.4.1.2, then updating from Version 5.4.1.2 to Version 5.4.1.8."