  We report the detection of anomalous brightness fluctuations in the multiple
image Q0957+561 A,B gravitational lens system, and consider whether such
anomalies have a plausible interpretation within the framework of cosmic string
theory. We study a simple model of gravitational lensing by an asymmetrical
rotating string. An explicit form of the lens equation is obtained and
approximate relations for magnification are derived. We show that such a model
with typical parameters of the GUT string can quantitatively reproduce the
observed pattern of brightness fluctuations. On the other hand, explanation
involving a binary star system as an alternative cause requires an unacceptably
large massive object at a small distance. We also discuss possible
observational manifestations of cosmic strings within our lens model.
