Thousands of people watched a film posted in its entirety to YouTube by its US distributor before the apparent mistake was tackled.
Sony Pictures Entertainment had labelled the video as being a trailer for the movie Khali the Killer.
But its 90 minute duration acted as a giveaway that the upload contained more than just highlights from the film.
The video was wiped after being online for more than six hours but not before news of its availability had spread.
CBR.com – which seems to have been the first news site to report the discovery – described it as an “epic mistake”.
Members of the public also made fun of the find via social media.
Sony has not responded to the BBC’s request for comment.
The low-budget film – which is about a Los Angeles-based hitman – had previously attracted little attention, despite having already been released in parts of Europe and playing at film festivals.
That led some members of a Reddit discussion to question whether the “accident” was in fact a publicity stunt.
“It takes much longer to upload a feature-length film than a trailer. Presumably, someone would have asked why it’s taking so long,” wrote one.
But this is not the first time Sony has made such a mistake.
In 2014, the company posted a much higher-profile film – The Amazing Spider-Man 2 – to its South Korea YouTube account.
In any case, Khali the Killer’s director has been making light of the latest debacle, on his own social media feeds.
Sony posts whole movie on YouTube in trailer’s place