
We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from SuperKamiokande contained events and from SuperKamiokande and MACRO upgoing muons. We have reanalysed the proposed solution to the atmospheric neutrino anomaly in terms of nonstandard neutrinomatter interactions (NSI) as well as the standard nu_mu > nu_tau oscillations (OSC). Our statistical analysis shows that a pure NSI mechanism is now ruled out at 99%, while the standard nu_mu > nu_tau OSC mechanism provides a quite remarkably good description of the anomaly. We therefore study an extended mechanism of neutrino propagation which combines both oscillation and nonstandard neutrinomatter interactions, in order to derive limits on flavourchanging (FC) and nonuniversal (NU) neutrino interactions. We obtain that the offdiagonal flavourchanging neutrino parameter epsilon and the diagonal nonuniversality neutrino parameter epsilon' are confined to 0.03 < epsilon < 0.02 and epsilon' < 0.05 at 99.73% CL. These limits are model independent and they are obtained from pure neutrinophysics processes. The stability of the neutrino oscillation solution to the atmospheric neutrino anomaly against the presence of nonstandard neutrino interactions establishes the robustness of the nearmaximal atmospheric mixing and massiveneutrino hypothesis. The best agreement with the data is obtained for Delta_m^2 = 2.3*10^{3} eV^2, sin^2(2*theta) = 1, epsilon = 6.7*10^{3} and epsilon' = 1.1*10^{3}, although the chi^2 function is quite flat in the epsilon and epsilon' directions for epsilon, epsilon' > 0.
