We're wading into the always-murky waters of intellectual property law here, so, of course, there's no clear answer. The short answer is no, they don't have to get permission. The long answer is … but they usually do anyway.

For the filmmakers, it's about lawsuits and avoiding risk. For the companies, it's about protecting the brand.

"The rule is a product can be used within a movie without permission as long as the product is being used as was intended by the manufacturers without negatively defaming the product or manufacturer," say Scott Widerman and Mark Malek, attorneys who specialize in trademark and copyright law.

What that means for your question is that, technically, a filmmaker doesn't need permission if they only mention Facebook or Twitter without putting it in a bad light.

But the definition of "bad light" is debatable — or, more accurately, litigable.

For example, is it in bad light to show a film's villain using Facebook? What if she's using Facebook as part of her master plan for world domination?

Maybe, or maybe not. But it's likely that most filmmakers, especially big ones who have legal teams behind them, prefer not to risk it and just get permission.

Your mention of free advertising also raises the flip side of this. Depending on how the brand is used, a filmmaker might be able to come to a product-placement arrangement with the company. That would mean that, rather than just simply getting permission, they might be able to get the brand to pay for the mention. This gets a lot more complicated, though (as if it weren't complicated enough already).

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