Let a certain file is input to the two anti-virus utilities. The first utility reports that the object is infected, while the second utility reports the opposite result. First utility gives the correct result with probability 0.9 and the second with probability 0.7. If we consider that the probability of infecting a file the virus is 0.3 (probability that the file is not infected, respectively, equal to 0.7), determine the posterior probabilities of infestation of the file.