A computer implemented method to identify a derivative of one or more malicious software components in a computer system including: evaluating a measure of a correlation fractal dimension (CFD) for at least a portion of a monitored software component in the computer system, the CFD including a plurality of CFD values varying with a resolution of fractal dimension; and comparing the plurality of CFD values with a reference measure of CFD for each of the malicious software components, each reference measure of CFD including a plurality of CFD values varying with a resolution of fractal dimension, so as to identify one or more of the plurality of malicious software components from which the monitored software component is derived.