I'm using: CustomLog "/var/log/apache2/access_log" "%a %l %u %t \"%r\" %>s %b \"%{Referer}i\"" And I occasionally see this right around the time the CPU starts running at 100%: :: - - [27/Aug/2010:12:28:01 -0700] "GET /favicon.ico HTTP/1.1" 200 - "-" %a is supposed to be an IP address, so what IP address is "::"? I'm only somewhat familiar with IPv6 but I've never seen "::" before.