The update schedule for Snow Leopard has been:
- 10.6 - August 28, 2009 (release date)
- 10.6.1 - September 10, 2009
- 10.6.2 - November 9, 2009
- 10.6.3 - March 29, 2010 (revised April 13, 2010)
- 10.6.4 - June 15, 2010
This last update included an update to XProtect to protect against OSX.HellRTS (aka OSX/Pinhead-B). This has doubled the size of the file.
Most Mac malware solutions protected against OSX/Pinhead-B by the end of April. Waiting for an OS update to protect against malware could prove costly if this backdoor steals your personal information not least because XProtect only scans download (not installed) files.