  We consider the supersymmetric approach to gaussian disordered systems like
the random bond Ising model and Dirac model with random mass and random
potential. These models appeared in particular in the study of the integer
quantum Hall transition. The supersymmetric approach reveals an osp(2/2)_1
affine symmetry at the pure critical point. A similar symmetry should hold at
other fixed points. We apply methods of conformal field theory to determine the
conformal weights at all levels. These weights can generically be negative
because of non-unitarity. Constraints such as locality allow us to quantize the
level k and the conformal dimensions. This provides a class of (possibly
disordered) critical points in two spatial dimensions. Solving the
Knizhnik-Zamolodchikov equations we obtain a set of four-point functions which
exhibit a logarithmic dependence. These functions are related to logarithmic
operators. We show how all such features have a natural setting in the
superalgebra approach as long as gaussian disorder is concerned.
