Is Twitter being powered by a stealth web server? Or is its tech team just friendly? The question is raised by Netcraft, which conducts a monthly survey of the Internet to track the number of web sites and the technologies they use. Netcraft's Web Server Survey has been compiling growth data since August 1996, using an agent similar to a search "bot" that scoots around the web, gathering information on more than 230 million web sites. When it encounters a site, the Netcraft agent asks "What server software are you running?" Most times, the server will answer "Apache" or "Microsoft IIS."
But not Twitter, which just says "hi." This practice, known as server spoofing, is seen in Netcraft's Twitter.com site info. Twitter is not the only site to intentionally alter server headers, with security concerns cited as a motivation in some instances. In other cases, services have used spoofing in a bid to influence Netcraft's server market share data. Others are more playful, such as the group of sites identifying their server as ZX_Spectrum/1997 (Sinclair_BASIC), which was an 8-bit personal home computer released in 1982, but it was discontinued two years before the World Wide Web even existed.
For what it's worth, the hosting history in Netcraft's site report suggests Twitter is running a particularly sociable version of Apache.