I've read about the 616 and also 606. It appears that the 616 comes from the earliest copy that we have. It has only recently been legible with new technology though. The following is copied from Wikipedia:
"It should be noted that the Book of Revelation (ed:-s) was not written in Hebrew or Latin but in Greek, and virtually any name can be turned into 666 or 616 by first using an "alternative" spelling of that name in one arbitrary language and then translating that word into a second arbitrary language and then using an arbitrary set of numerology rules. "
