• In a lawsuit filed in Seattle, Wash., federal court, Zillow is claiming that competitor Trulia stepped on Zillow's patent for calculating home values.
• The online competitors offer ways for current information to be added to a house's file so online valuations can be kept up to date.
• Zillow's allegation is that a method it patented is the way Trulia gets updated information into its calculations.

From the report:

Real estate data site Zillow filed a patent infringement suit against Trulia ... claiming its chief competitor infringed on an existing patent that fuels the website's ability to provide up-to-date real estate estimates to users. ...