I don't think it is selfish at all. You put in the work to learn something and you are giving it away for free. People who are earnestly searching for information will find it one way or another.
I'd consider selfish to be learning something and keeping it all to oneself.
Maybe its a PR move for Microsoft more than anything. "Windows 8 has a built-in anti-virus and is more secure than ever!"
I feel like Windows gets targeted the most because there are just so many computers running it. If 80% of computers out there ran OSX I wonder if anyone would give a shit about the next vulnerability in Windows.
Anti-viruses will always be necessary. There is money to be made in sending spam, running bot nets, and mining data. Regardless of what operating system you are running I'm sure there is someone out there who could find a vulnerability if he or she was motivated enough. Is this more of a PR move? Whenever you talk to Mac users they seem to flaunt the fact that they are virus free or is it that no one bothers since so few people have macs compared to pcs?
I'd consider selfish to be learning something and keeping it all to oneself.