In blogging, ping is an XML-RPC-based push mechanism by which a weblog notifies a server that its content has been updated. An XML-RPC signal is sent to one or more "ping servers," which can then generate a list of blogs that have new material. Many blog authoring tools automatically ping one or more servers each time the blogger creates a new post or updates an old one.
Open ping servers, like VeriSign's Weblogs.com, let other web-services subscribe to a list of blogs that have recently pinged them. Blog search engines can provide fresh results very quickly by polling only the newly-updated blogs. Similarly, aggregators use results from ping servers to tell subscribers which items on their subscription lists have fresh material.
In addition to open ping servers, there are an increasing number of proprietary ping servers that gather information only for their own applications. Most of the major blog search engines operate such ping servers.
Unlike open ping servers, proprietary servers with their own subscription applications have no incentive to share their received ping data directly with other servers, which may offer competing services. As these servers do not share their data, bloggers have to ping a large number of individual servers to receive the desired publicity. As a result, bloggers have turned to services such as Ping-o-matic, which pings multiple proprietary ping servers.
Creators of ping spam and/or spam blogs may hope to benefit by creating pages to turn up in web searches for popular keywords. Typically, an individual spam post links to some external page that displays Google ads or offers a product for sale.