This story is part of War in Ukraine, CNET's coverage of events there and of the wider effects on the world.

As news broke that Russia had invaded Ukraine, Twitter user @AndreyZhukovv posted a video of buildings blanketed in darkness. A bright flash lights the sky followed by a loud boom. The user described the video with one word: Mariupol.

Before long, the video had racked up millions of views. Because Mariupol is a city in south eastern Ukraine, journalists chimed in, asking if they could republish the video. Sad face and prayer hand emojis filled the replies. "I really wish this was one of those stupid edited videos," one user wrote. 

The video, it turns out, was misleading. A handful of Twitter users figured out the clip posted on Wednesday came from an older TikTok video. The January video bore a different caption in Russian: "Lightning strike into the power station!"

By Friday, Twitter had pulled the video for violating the site's rules. The company has rules against misleading media, which bar users from sharing content with false context or fabricated footage. But the damage had already been done. The video had 6 million views before Twitter removed the tweet.

Manipulated and misleading videos have long plagued social media. In a famous example, a video posted to Facebook was slowed to create the impression Speaker of the House Nancy Pelosi was drunk, sparking more scrutiny over how social networks respond to misleading content. More-sophisticated forgeries, known as deep fakes, use artificial intelligence to create videos of people making statements they didn't say. 

During times of crisis, the viral potential of misleading videos, like the one posted by @AndreyZhukovv, underscores the challenge Twitter and other social media platforms face in tamping down on unintentional misinformation and deliberate disinformation. Posts spread quickly before platforms can go through the process of reviewing them for removal. 

BNO News, which has a Twitter verified badge, used the misleading video from @AndreyZhukovv in a tweet that read, "BREAKING: Massive explosions hit the Ukrainian port city of Mariupol." The video reshared in that tweet had nearly 3 million views, along with thousands of retweets and likes before Twitter took down the tweet on Wednesday for violating its rules. 

The BNO News tweet also appeared in Twitter's pilot program Birdwatch, which allows users to fact-check and add notes to tweets. "This is an old video posted on Tik Tok depicting [lightning]. Not explosions or bombs," read one note. (The note misspelled the word lightning as lighting.) 

Twitter says it's trying to combat false and misleading content. 

"We're proactively monitoring for emerging narratives that are violative of the Twitter Rules, including our synthetic and manipulated media policy and platform manipulation policy, as the situation develops," a spokesman said in a statement.

People share misleading information for different reasons. Some people get duped into thinking that what they see in a video is real, without considering there's a possibility the footage may be altered or taken out of context. 

Mike Caulfield, a research scientist at the University of Washington Center for an Informed Public, said using old video footage is a common technique to trick people on social media.

"It's a tactic that is used by both people who are in search of clicks and shares and by people who are sometimes engaging in active disinformation campaigns," Caulfield said. 

Neither @AndreyZhukovv nor BNO News responded to requests for comment. 

Ottawa resident Nicole Anna Rutkowski was "shocked" when she saw a video on Twitter that depicted a fiery explosion claiming to be in Ukraine. For a moment, she thought the video "could be real."

But Rutkowski, a doctoral student in clinical psychology at the University of Ottawa, has become more skeptical about what she sees on social media, particularly after she read an article about how Russian bots spread misinformation in Canada.

"I had now become a skeptic and so had my partner when I showed [the video] to him," she said in an email. She was suspicious because none of the mainstream news outlets had shared the video and thought it was "weird" the account used fluent English even though the user identified the footage being shot in Ukraine. 

Rutkowski's gut feeling was right. The Twitter video, which has also been fact-checked on Facebook, was old footage of a 2015 explosion in Tianjin, China. It had nothing to do with Russia's attack on Ukraine, Reuters reported. Rutkowski said she was able to link the video to the explosion in China because another Twitter user mentioned it in a comment.

"I googled the explosion and there indeed was the exact same video," she said. "I was inspired by the gentleman and posted under a bunch of the accounts reposting the video that it was fake news with a screenshot of the Wikipedia page of the Tianjin China explosion." 

Reading the replies to a video is one way to figure out if the clip may be old footage. But some Twitter users sharing misleading videos hide replies or limit who can respond. Twitter added those tools to partly combat abuse and spam. 

One tweet posted Wednesday by @Bajrangi_lama claimed to show the Ukrainian army shooting down a Russian jet. The user hid the replies to the video that said it was an old video. Twitter users can view hidden replies if they click on a gray icon next to the time and date of a tweet. @Bajrangi_lama didn't respond to a request for comment.

Twitter didn't answer questions about whether its tools are being abused to fuel the spread of misinformation.

Facebook said it will take down content that violate its rules and is working with third-party fact checkers to debunk false claims. If a fact checker rates a piece of content as false, it's shown lower in the Feed so fewer people see it. The company is also adding labels on false content and applying labels to state-controlled media publishers. "We are taking extensive steps to fight the spread of misinformation on our services in the region and continuing to consult with outside experts," a Facebook spokesman said in a statement.

A spokeswoman for short-form video app TikTok said it would remove any misleading videos that violate its misinformation policy.

Caulfield said in times of crisis there's often pressure among social media users to be first in their group of friends or followers to share content, leading them to make "a lot of bad decisions." But people should ask themselves about where any piece of content they see on social media comes from and if it's been verified. If they can't answer these questions, he said, they should wait to share.