The "Fiveten" Blocklist (blackholes.five-ten-sg.com) was a combination anti-spam blocking list run by Carl Byington, publishing under the name of "510 Software Group." This blocking list has been available since at least February, 2001, and it appears to have been retired as of April 2012.
As of late April, 2012, any attempt to look up an entry on the list results in output indicating that "The blackholes.five-ten-sg.com list is retired. No ip address is listed here." Meaning, the list is no longer in operation.
I had previously written about this list back in October, 2007, and my 2007-2008 DNSBL statistics project data showed that the list may not be suitable for broad production use if one wishes to receive requested email messages. The list has been up and down at various other times, most recently being taken offline for a period in November 2010.
(Hat tip: Word to the Wise)