Unhappy Windows 10 users in Illinois are taking Microsoft to court, claiming that problems caused by the Windows 10 upgrade show that it was negligently designed, that Microsoft fraudulently failed to disclose its defects, and that the upgrade is unfit for purpose.

In a break from tradition, Microsoft offered Windows 10 as a free upgrade to Windows 7 and 8.1 for the first year of its release. This unusual offer was matched with a set of increasingly aggressive promotions within Windows itself. In the early days of the upgrade offer, there were even some users reporting that it installed automatically.

Three plaintiffs claim specific harm was caused by the operating system. Stephanie Watson claims that Windows 10 installed without her choosing to accept it. The upgrade destroyed some data, caused such harm that Geek Squad was unable to fully repair the machine, and forced the purchase of a new system.The suit claims that "many" consumers have had their hard drives fail because of the Windows 10 installation, and that the operating system does not check "whether or not the hard drive can withstand the stress of the Windows 10 installation."

Robert Saiger agreed to the upgrade. However, this caused Saiger's existing software to cease functioning, and it also caused some data loss. Saiger incurred costs reconstructing and replacing the lost data. The suit claims that the Windows 10 upgrader does not bother to check for hardware or software compatibility prior to installation.

Howard Goldberg eventually accepted the upgrade after declining it for six months. The download and installation failed three times, with Goldberg claiming that this "damaged" his PC, causing data loss, loss of revenue, and incurring costs to repair the system.

Similar problems were apparently so endemic and widespread that they show Windows 10 breached its implied warranty of merchantability according to the suit. The suit claims that there should have been greater warnings that it may damage PCs or data and that it should have told consumers to make backups. It further alleges that Microsoft was negligent; that the company failed to "exercise reasonable care in designing, formulating, and manufacturing" the upgrade, and moreover that Microsoft knew Windows 10 to have "potentially harmful propensities."

Per the suit, there are hundreds or thousands of others who have suffered similar problems and incurred similar costs. It proposes a class of harmed users—Americans (that installed the Windows 10 upgrade on any computer equipped with Windows 7 "or earlier operating systems," though no earlier operating system offered the upgrade) who suffered loss of data or damage to software or hardware within 30 days of the installation.

The lawsuit says that Microsoft owes more than $5 million in damages, both actual and punitive.

Microsoft, in response, says: