itunes commercial podcast piracy security
The security must be provided by the content provider, though iTunes can access password-protected podcasts. The content provider sets up password protection via HTTP authorization and/or SSL encryption. It's then as secure as SSL, which is the standard for encryption on the Web, used by Websites for secure transactions, such as stores, credit cards, etc.

See this link for more on setting it up.

Once you've set it up, you can access the podcast via iTunes by clicking a link on the content provider's site. iTunes gives you an authorization dialog to access the podcast:



Apple says it does not list password-protected podcasts on the iTunes Store.