Web Service Security issues

[dntchaseme]

I intend to create a webservice which provides a service for updating a clients data at a remote location. In other words, this service will update values stored in the database. Other than making sure that a user may not access others' data, are there any security concerns i should be wary of by allowing a web service to interact with a database?(although it will have to use the systems database handler class to do so)
I intend to secure the connection and also implement a verification method of the user.

Imran Hashmi
www.visionstudio.co.uk
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