It's worth noting that other billionaire investors were buying Apple shares in Q3, including Ole Andreas Halvorsen of Viking Global Investors and John Armitage of Egerton Capital. These mixed signals beg the question: Is Apple still an attractive investment, or should you follow Buffett's lead and take some profits?

Warren Buffett's Berkshire Hathaway has created tremendous wealth for shareholders, and a key component of those returns stems from buying shares of strong businesses at attractive prices relative to their estimated worth.

The tech giant has been testing the upgraded software on iPhones, iPads and Macs, and it will ultimately replace the Siri interface that users rely on today.