  We consider the valuation problem of an (insurance) company under partial
information. Therefore we use the concept of maximizing discounted future
dividend payments. The firm value process is described by a diffusion model
with constant and observable volatility and constant but unknown drift
parameter. For transforming the problem to a problem with complete information,
we derive a suitable filter. The optimal value function is characterized as the
unique viscosity solution of the associated Hamilton-Jacobi-Bellman equation.
We state a numerical procedure for approximating both the optimal dividend
strategy and the corresponding value function. Furthermore, threshold
strategies are discussed in some detail. Finally, we calculate the probability
of ruin in the uncontrolled and controlled situation.
