Ever since he took over as the CEO of Microsoft in February 2014, Satya Nadella has championed the “mobile-first, cloud first” strategy. Lack of major apps was a major issue with Windows 8 as well as Windows Phone. Nadella came up with Universal Windows Platform that will allow developers to create a single app that works seamlessly across all form factors.

Windows 10 Universal Apps Won't Work, Says Steve Ballmer

Enable Windows Phones to run Android apps

Even though Windows 10 is off to an impressive start, Nadella’s predecessor Steve Ballmer says the universal apps strategy “won’t work.” Speaking at the company’s annual shareholder meeting, Ballmer said instead of using universal apps, Microsoft should develop software to let customers use Android apps on Windows Phones. Ballmer is one of the largest shareholders of Microsoft.

When a shareholder asked Satya Nadella how he plans to address the lack of apps on Windows Phone, Nadella said the universal apps strategy would entice developers to create new apps that work across all Windows devices. That’s when Ballmer chipped in, stating “that won’t work.” Microsoft shares have skyrocketed 73% since August 2013 when Ballmer announced his plans to step down as the company’s CEO.

Windows 10 Mobile to arrive later this month

The former Microsoft CEO also criticized the way the Redmond-based company reports its revenues and margins from cloud and hardware businesses. Microsoft reports a “run rate” on its cloud services instead of reporting actual revenues. The company recently reported 44% gross margins on its commercial cloud services business, without revealing total profits from the cloud or hardware businesses. Nadella expects cloud revenues to reach $20 billion by 2018.

Ballmer pointed out that cloud services and hardware have much lower gross margins than Microsoft’s legacy software business. He called the company’s reporting of revenue run rate “bullshit.” As of October, Windows 10 runs on 120 million devices. Though its adoption has slowed in recent weeks, the launch of Windows 10 Mobile later this month is expected to fuel the adoption.

Satya Nadella aims to have Windows 10 installed on at least one billion devices by 2018, including PCs, smartphones, tablets, Xbox consoles, and other devices.