InstallShield Software has filed a lawsuit against Wise Solutions, alleging that the company engaged in electronic espionage on at least 903 occasions.
Chief finance officer Tyler Sheffield said InstallShield is asking for unspecified damages.
Both InstallShield and Wise Solutions develop and sell tools to software development companies.
Sheffield said the US Attorney's Office and the US Federal Bureau of Investigation are in the middle of investigations into Wise's allegedly illegal activities, but he was unsure when, or if, a criminal complaint will be filed.
In its civil complaint, InstallShield contends that it discovered information indicating that from 1 July 2002, until 23 June 2003, Wise obtained access to InstallShield's file transfer protocol (FTP) server using the usernames and passwords of two InstallShield employees, as well as with an "anonymous" account.
Sheffield said neither InstallShield nor law enforcement officials believe that the two employees were involved with Wise's activities.
Using the confidential usernames and passwords of the two InstallShield employees, Wise allegedly downloaded 903 files. Many of the files contained proprietary and confidential information, including two mailing lists containing the business names, individual contact names and addresses of 109,900 InstallShield customers and prospects.
"We match up very closely as competitors, so it's a goldmine to get access to this," Sheffield said.
"Wise has a reputation of honesty and integrity, and nothing like this has every happened before in our history," said Pat Ziarnik, Wise's chief legal counsel.
"We know for a fact that their customer list was publicly available - we determined that through a forensic investigation - but we are conducting an internal investigation to see what happened."
However, InstallShield spokeswoman Ariana Nikitas insisted that its customer list was not publicly available," she said.
In addition, Wise allegedly obtained unauthorised assess to and downloaded InstallShield's confidential advertising and marketing materials, then used that information to create an almost identical ad campaign, according to the complaint.
Sheffield and Ziarnik said Wise agreed to an injunction prohibiting it from engaging in these activities until the matter is resolved in court.
A court date has not yet been set.
Linda Rosencrance writes for Computerworld