Well, that was stupid

In the course of doing some minor site maintenance work last night, I left in an extra ,OR in a RewriteCond statement in the root .htaccess file for this site. The side effect was to block access to the entire site for the day.

Doh!

See, I'd deleted a number of the lines that caught various referer spam and affiliate spam hits but did not change the new last line of the remaining list to elide the OR statement, which caused the entire structure to be true at all times.

Service has been restored. The webmaster will be flogged.