Except that I know from a large amount of experience the most common reason by far for outdated software is neglect.
As an expert in the field for 20 years, this bashing is ridiculous.
Many companies do not the latest and greatest intentionally. They don't upgrade unless there is a need. Don't fix what isn't broken. We are just now upgrading from Windows XP to Windows 7. It takes this long for all our internal software to be migrated and there to be a need.
This bug generally affects web servers and other applications using OpenSSL versions 1.0.1 through 1.0.1g. Apple's web servers used a previous version, 0.98. OpenSSL is just one of many components of Linux /unix that Apple uses. many of which are the latest versions, many of which aren't. Apple has a team which decides whether or not to use certain versions, and there is no need to use the latest if it has new features Apple doesn't use, or are bloated, or use too much system resources. Use the one that is better.
Apple might have gotten lucky on this, they might have been smart. Nobody but Apple internally knows. Apple just released a bulletin to let people know, because OS X IS Unix. It's necessary to say they aren't affected, just like if Red Hat wasn't affected, they would say so too.
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Does this mean using Safari browser is not affected and what about Chrome, are both not affected on my Mac or just safari?
It's a web server thing, nothing to do with a web browser. If you've visited sites like Google, Yahoo, Amazon, your password or other information may have been compromised. 2/3rds of websites use the latest Apache web server, thus they were all affected.