Whether we should use single on multiple sites?

Hello,
One of my clients have come up with a strange requirement. They have multiple websites showing more or less same db based information.

Now they want, a single db to be used on all sites. For example. www.mywebsite.com has the db, now his second website www.mywebsite2.com, will connect to the db for the 1st site and fetch information.

I would like suggestions as to whether it will be a good way of doing things? What security concerns we might have and how can we overcome them?

I look ahead to your comments.

Thanks