  The massless one-loop box integral with arbitrary indices in arbitrary
space-time dimension $d$ is shown to reduce to a sum over three generalised
hypergeometric functions. This result follows from the solution to the third
order differential equation of hypergeometric type. To derive the differential
equation, the Gr\"obner basis technique for integrals with noninteger powers of
propagators was used. A complete set of recurrence relations from the Gr\"obner
basis is presented. The first several terms in the $\varepsilon =(4-d)/2$
expansion of the result are given.
