Spiders are search engine's. They send "crawlers" out to grab new data, also known as spidering data.
WOL data is cached, it'll never be 100% correct, view the "details" link to get a 100% (well as close as can be) view of current users.
As for adding a header,there are a couple of ways, the easiest is to just use the image tag in the CP -> Display Options -> General -> HTML Includes Tab -> Default Header area
