Taxonomy is a major concern to viral genomics as there are 3186 viral species officially recognized by the International Committee on Taxonomy of Viruses (ICTV) (53) and 4834 complete genomes from both official and provisional viral species available from INSDC databases. The NCBI Pairwise Sequence Comparison (PASC) tool was developed to assist in the classification of viral genomes based on global and/or local alignments between genomes (http://www.ncbi.nlm.nih.gov/sutils/pasc/). The scope of this tool has been expanded to include a number of virus families and other taxonomic groups, and it has been used to help support the demarcation of new taxonomic criteria (54–57).
