The database is about as secure as anything else on that server (they're all just files in the end).
From the folks that bring you Zend:
http://www.zend.com/zend/trick/tricks-sept-2001.php
(check out the last paragraph if you wish to skip the tests involved). Although if you read the entire article, you may find your answer in there as well...
Personally, I wouldn't look to store files in the database:
Word files are about 30k on average. Versus a file name could be as long as 100 bytes.
You're probably not going to be comparing blobs to other blobs or doing searches within a blob. Basically, I doubt you'll be issuing any queries against the entire file itself (and if so, how fast will it really be versus indexing the data seperately?).
You're limited to the databases file structure versus your own (yes, you CAN issue your own file structure and naming convention). This would allow you to control specifically where the files are located, how they are accessed/protected, and can later shuffle the files around to another server if needed. You could even back them up if you desired.
Performance. It'll be faster to let the native file system handle the storing of the file (which is what it does best) versus the database engine. Again, backup should NOT be an issue - either tweak the back up settings or contact your provider to update them. Backing up a database requires the database engine to be paused or shutdown (unless doing shadow reading). Basically, database backing up can be problematic if not addressed specifically (make sure your backups work before relying on this method).
Security is an issue regardless of where you store the files. If you really need security, then you need encryption.
If you need to update a file, you can copy the file in place instead of issuing database commands (you'd have to probably create a tool to go in and figure out what ID needs to be updated and then issue the update command with your file data).
I've had to tackle this problem with storing e-books (lots of them and they averaged from 1mb up to 10mb). It required a lot more work and thinking to figure out the naming conventions and directories to save the files to, but once we figured it out, it was easy to maintain and backup.
