If you are running 4.0.2 already, simply download the latest Security patch: 4.0.2 Suite PL1 from the Patches section in the Members Area, extract the 5 patch files, then upload these files making sure to overwriting the existing files. This will update your version to the latest patch release. The patch files are:
[code]
includes/class_core.php
includes/functions_forumdisplay.php
includes/functions.php
includes/version_vbulletin.php
vb/legacy/thread.php[/code]

If you are running 4.0.1, you will need to do a full upgrade to 4.0.2 PL1 upgrade with this here [url=http://www.vbteam.info/vb-4-0-releases/38301-vbulletin-suite-v4-0-2-incl-keygen-php-null-dgt.html]4.0.2 Null DGT[/url] - For suite, and for forum only users upgrade to [url=http://www.vbteam.info/vb-4-0-releases/38222-vbulletin-forum-v4-0-2-php-null-dgt.html]4.0.2 Forum Null DGT[/url] then apply the patch!!!

Only doing this to protect users here at vBTEAM. Enjoy!