Pity us parents during the winter flu season. As if the usual viruses perpetually afflicting our children this time of year weren’t bad enough, Walt Disney Co. has decided to inflict a whole new contagion: “Frozen.”

The animated smash, which has slid past $900 million at the global box office, has permeated every cell of preadolescent brains worldwide since bowing in theaters last November. Symptoms include compulsive soundtrack-singing, incessant dialogue-quoting and an insatiable need for “Frozen” merchandise.

This malady also manifests itself on YouTube, where my 5-year-old ceaselessly clicks on any and all videos associated with the movie. Obsessive as that may seem, he’s got nothing on the many “Frozen” fans who have gone so far as to upload content they’ve created celebrating the movie.

It’s rare to see a film attract this level of online fanaticism. My son is particularly fond of the zillions of “Frozen” cover songs, many of them sung in different languages. He’s also watched his favorite character, Elsa, rendered as an ice sculpture and particularly enjoyed seeing her signature French braid lovingly re-created (though he doesn’t quite have enough hair to replicate it).

All this free marketing — or as it’s known on Madison Avenue, “earned media” — only makes “Frozen” even more profitable for Disney, which also pumps out its own “Frozen”-themed content as well via its official YouTube channel and on its branded website and apps. But the official stuff is dwarfed by the amount of fan-generated content.

There is a downside to this YouTube bounty; it’s not all entirely, as Madison Avenue also likes to say, “on brand,” even when it comes from the most well-intentioned “Frozen” fans (shouldn’t this community have its own name? … “Icicles”? “Frozenistas?”). Like the “brutally honest” rendition of one soundtrack song that sprinkles obscenities into the lyrics. Or the widespread piracy courtesy of cameras hidden in the theaters, which parse just about every frame of the movie into clips littered all over YouTube.

Thanks, “Frozen,” for helping me explain to my son what piracy is, though that probably wasn’t the point.

If it chose, Disney, or any other studio for that matter, could scrub YouTube clean of any content that didn’t come from the company. YouTube’s own Content ID system, and firms that specialize in online content monetization like Zefr, empower copyright holders to monitor any unauthorized appropriation of its content, and to collect audience data. A content owner has the choice of removing what it doesn’t like, letting it remain, or taking the next step — imposing ads on it that yield revenue.

And yet Disney seems to have taken a relatively hands-off approach to YouTube, placing little advertising on all this content. The studio seems to have borrowed its strategic mantra online from the chorus of “Frozen’s” hit single: “Let it go, let it go/can’t hold it back anymore … ”

The balancing act that content owners have to do with regard to YouTube — as well as other fan-friendly platforms like Tumblr — is a tough one. On the one hand, corporations must loosen their grip on their own product for their promotional benefit. On the other hand, ceding control can be a scary thing.

But erring on the side of a long leash is the right call. The DIY ethos of YouTube means allowing a mashup culture to blossom even if that impinges on fair use and brand values. The tight rein that studios typically keep on their intellectual property simply doesn’t fly here.

Of course, none of that helps my son get over “Frozen.” My best bet is to fight fire with more fire; what better way to dislodge that film from his mind then by introducing him to another.

But this won’t be easy. Told recently he was going to see “The Lego Movie” at the earliest opportunity, he replied, “Is Elsa in it?”