The lawsuit, filed in the US District Court for Massachusetts, also charges that Thomson has consistently engaged in unfair trade and business practices; misrepresentation; breach of contract; and monopolisation in violation of the Sherman Antitrust Act.

In a statement, Thomson categorically denied the allegations. The company says it intends to "vigorously defend itself against this baseless claim", which Thomson alleges is the result of a breakdown in negotiations over the future working relationship between the two companies.

CCBN, which offers a broad range of Web-based investor relations products and services to publicly-traded companies and the investment community including the StreetEvents service, was founded by Jeffrey Parker and Robert Adler. Parker, a former chairman and CEO of Thomson Financial, developed First Call and sold it to Thomson Financial in 1986. Parker, who left Thomson Financial in 1991, invited his former employer to be an investor and strategic partner in CCBN not long after it was founded in February 1997.

In a statement, Parker claims: "For more than four years, Thomson Financial, through its designees to CCBN's board of directors, received the most sensitive business information about our company and then used everything it learned - and more that it stole by breaking into password-protected sites - to create a directly competitive business."

The suit says Thomson Financial, having induced CCBN into a relationship of "trust and confidence, ...improperly used information obtained in their roles as fiduciaries [of CCBN], misappropriated CCBN corporate opportunities and improperly used their dominant market power to injure and steal [CCBN's] business."

CCBN is asking the court to order Thomson to:
* return to CCBN all proprietary material;
* stop competing with CCBN using information, know-how, or strategies acquired from CCBN in confidence or in a fiduciary capacity;
* cease logging onto CCBN Web sites without proper authorisation and under false pretenses; and
* award compensatory and treble damages, as well as any other relief the court considers appropriate.

Thomson has dismissed the suit as "an exploitive attempt by CCBN.com to discredit Thomson among its customers and investors".