COAs are used to identify genuine Microsoft software and computers that have been preloaded legitimately with the firm's operating system and other software.

However, following a year-long investigation into the eight companies in question, Microsoft revealed that they had been separating genuine COAs from PCs and re-using them on systems loaded with pirated copies of Windows, or to authenticate other Microsoft software.

The decision to take legal action against the resellers forms part of a larger ongoing campaign by the software giant to protect its intellectual property.