Statistical tests were applied for the set of viral proteins in view of the host cellular protein for each cluster (or Pfam family collection). We applied statistical confidence tests (P-values) based on the non-parametric Kolmogorov-Smirnov (KS), Student t-test and the hypergeometric distribution tests. The KS test is based on the maximum distance between the two cumulative curves based on the separated viral and host proteins and viral and metazoan for the TAILs and IDOLs.