NetWitness did not name the companies or agencies whose computers were negotiated. The Wall Street Journal has said that the affected companies included Merck & Co., Cardinal Health Inc., Paramount Pictures and Juniper Networks Inc. Merck and Cardinal Health has said in statements published on Thursday that one computer in each company was among those in the botnet, but no sensitive information was taken. The other two companies did not return messages from The Associated Press.

The victims did not appear to have been specifically targeted, unlike the recent computer attacks on Google Inc. that have prompted the Internet search leader to threaten to pull its business out of China. That was an important distinction, because it has shown how online secrets can fall into the wrong hands even when criminals were not necessarily looking for them.