Nielsen clients using the research firm's Nielsen U Virtual Classroom got a lesson Thursday that some may not soon forget. In notice sent to customers using the system, Nielsen warned that emails
sent to classroom participants by a "third-party email distribution provider" was "compromised by a virus." The email, Nielsen said, "included a number of hijacked hyperlinks within the email," and
cautioned its customers not to click on any links within the email, and to delete them immediately.
"These links are redirecting viewers to a number of outside websites, which are in no way
related to or endorsed by The Nielsen Company," the notice, added. "We are working with this provider to discover the cause of this occurrence and to ensure it does not happen again. We sincerely
apologize for this unfortunate incident."