The mail security program does use 2 seperate licenses. 1 is for the virus definitions, while the other is for the Premium Anti Spam. If you purchase the Enterprise edition of Symantec then that license will work with the Mail Security for receiving virus defintions. If you do not wish to use the Enterprise edition, then you would need the Mail Security license, and the premium anti spam add-on. These would provide you with virus defintions, and spam protection.
From your description, you have premium anti spam licensed, and no content. This would mean that your spam is being removed, but the virus defintions will not update.
Hope this helps.