[4] On April 18, 1989, Quarterdeck was awarded a US software patent that allowed multiple windowed PC applications under MS-DOS.

In order to diversify the company's product offerings, Bastiaens began an ultimately unsuccessful acquisition spree.

[12] Both Landmark and Vertisoft had extensive revenues from direct-marketing of third party products through telemarketing and direct mail.

[13] Bastiaens resigned in August 1996, and Quarterdeck continued under acting Co-CEOs King R. Lee, and Anatoly Tikhman, the former CEO of Vertisoft.

[11][14] In 1998, with its DOS utilities market all but collapsed, Quarterdeck was acquired for $0.52 per share by Symantec (the Norton Utilities company), which discontinued support of some Quarterdeck products, e.g., Mosaic, and integrated others into larger offerings, e.g., CleanSweep, which became part of Norton SystemWorks.