None of these with the possible exception of Google has a Stellar Security Record. With M$ it's a great month if there are only 8 Hot Fixes to apply and quite often many more that can have been reported up to 5 years previously and M$ has never got around to fixing till now.
With all Closed Source you have no idea what "Backdoor? Buggy? Amateur coding [in some cases]? Foreign developed?" problems exist or what Holes are already known and we are not told about.
Security through Obscurity is no security at all.
Col
