Barcodes of five representative human viruses: (a) HIV, (b) Enterovirus, (c) Rabies virus, (d) SARS Coronavirus, and (e) Hepatitis B virus.

<p>For each barcode, the x-axis is the list of all unique combinations of 4-mers arranged in the alphabetical order, the y-axis is same kind of virus joint genome axis contracted by 2,000 fold, and the gray level shows the frequency of each k-mer within a 2,000 bp window in the corresponding location.