Those obsessed with where Google ranks their Web site have a new topic to mull over: cloaking.

Google's Matt Cutts, in charge of much of the search giant's antispam efforts, tweeted over the past week that Google plans to take a closer look at the practice of "cloaking," or presenting one look to a Googlebot crawling one's site while presenting another look to users. This can include "serving a page of HTML text to search engines, while showing a page of images or Flash to users," according to Google's Webmaster Central help pages, but Cutts implied that Google was looking beyond page content in its renewed emphasis on cloaking by suggesting that Webmasters "avoid different headers/redirects to Googlebot instead of users."

As with just about any change that Google announces to its secret and powerful Web ranking recipe, Webmasters immediately started to freak out (to a certain extent) over what exactly Cutts meant in his tweet. Search Engine Land summed up some of the reaction, which initially appears to center on whether or not legitimate sites that are serving up rich media files will get caught up in a Google purge, or sites that present mobile-optimized content to those with mobile browsers will get punished.

Still, it's rare for Cutts and Google to announce this type of algorithmic shift so publicly, which implies they're giving Webmasters a warning shot in order to reexamine their sites before the ranking changes go into effect, and that rankings may be a little fluid as it rolls out.