Google Inc. is penalizing Overstock.com Inc. in its search results after the retailer ran afoul of Google policies that prohibit companies from artificially boosting their ranking in the Internet giant's search engine.

Overstock's pages had recently ranked near the top of results for dozens of common searches, including "vacuum cleaners" and "laptop computers." But links to Overstock on Tuesday dropped to the fifth or sixth pages of Google results for many of those categories, greatly reducing the chances that a user would click on its links.

The incident, according to Overstock, stemmed in part from its practice of encouraging websites of colleges and universities to post links to Overstock pages so that students and faculty could receive discounts on the shopping site. Overstock said it discontinued the program on Feb. 10, before hearing from Google, but said some university webmasters have been slow to remove the links.

Internet search experts say that sites associated with educational institutions, which come with ".edu" in their Web addresses, are often considered by Google's search algorithm to be more authoritative than commercial sites. Experts say educational sites rarely link to commercial sites, so a shopping site can surge in Google rankings if an .edu page links to it.

"Google has made clear they believe these links should not factor into their search algorithm," said Patrick Byrne, Overstock's chief executive, in a statement. "We understand Google's position and have made the appropriate changes to remain within Google's guidelines."