This sounds like paid propaganda. This is not the first time that big corporations try to tarnish the reputation of open source software and they're repeatedly proven wrong. Open source software is more secure because it has more eyeballs and there is a shared interest across multiple companies to fix any bug which arises.

Closed source software is often insecure and relies on security through obscurity. This creates opportunities for employees (and ex-employees) to exploit the software for their own benefit. Sometimes they introduce vulnerabilities or avoid fixing known vulnerabilities intentionally. Most of the time, big companies don't even realize that their systems are being exploited in thousands of different ways at any given time.