In the last week of October, commercial real estate brokers all over the country received a package via snail mail from CoStar Group. Inside was the informational equivalent of a dirty bomb — the latest salvo in the data giant’s legal battle against its main rival, Missouri-based Xceligent. When brokers opened the UPS envelope, they found a brochure with a carefully assembled selection of news clippings and letters about Xceligent’s alleged theft of CoStar’s data. It also included a congressional letter and news reports about human and sex trafficking.