Whether it's faking a letter from a chief executive to alter a corporate strategy, or staging a car crash to imply a faulty vehicle, fake news that generates headlines can — and has — hurt a company’s bottom line, pushing the stock price down and setting off a public relations nightmare that is, in many cases, irreversible.

Now, many companies are striking back, hiring third-party firms with an army of human monitors and the latest artificial intelligence to trawl social and traditional media in search of viral posts that could send shares into a downward spiral.

“Containing the spread of disinformation, especially for a brand or public figure under attack, is a race against time,” said Jean-Claude Goldenstein, founder of CREOpoint and developer of a business intelligence technology that aims to curb the fallout from fake news.

“It takes preparation to put out specific fires in their tracks, way before they grow into wildfire and cause irreversible damage,” he told NBC News.

One case in point: A video surfaced in January purportedly showing a Tesla “self-driving vehicle” slam into a robot prototype at CES, a consumer electronics show heavily attended by tech reporters from across the globe. It wasn’t long before the video went viral, with a number of outlets running headlines claiming “Self-driving Tesla car kills robot.”

The only problem was that the video was completely fake. Tesla does not currently have a self-driving model, and the robot that was “killed” was in fact part of an elaborate publicity stunt conjured up by the Russian firm that developed it.

Or was it?

Some experts in the disinformation field suspect the caper was not any kind of bot promotion but rather a deliberate attack on the American stock market by "foreign actors" trying to undermine consumer acceptance and trust in self-driving cars and drive down stock prices in companies that develop them.

As automakers and billion-dollar startups such as Lyft (which went public this month), Uber (which just filed paperwork for its own IPO) and Tesla stake their future on a consumer shift to autonomous driving, public confidence in self-driving is a crucial factor in that success.

With three out of four Americans saying they are afraid of self-driving cars, a robot getting “killed” by Tesla likely did little to allay that negative perception.

More recently, footage started to circulate online Sunday that showed a Tesla Model S car burst into flames in a Shanghai parking garage. Tesla announced it would investigate the video, which had been shared from the Twitter handle @Shanghaijayin. While there is no indication that the video was faked or intended to damage Tesla, it comes from an account that frequently posts footage of electric vehicle fires.

The incident drew international attention, and by Monday morning Tesla shares had slipped. The company's chief executive, Elon Musk, questioned the media interest, tweeting on Tuesday: "Over a million combustion engine (it’s right there in the name!) car fires per year & thousands of deaths, but one Tesla car fire with no injuries gets biggest headlines. Why the double standard? This is a real question."

Users on a chat forum named Tesla Motors Club questioned whether the video was staged, saying the origins of the fire seemed "very nontypical" and theorized that the bad press surrounding a burning Tesla would help Chinese-made electric cars gain an edge in the world's largest auto market. Other users dismissed such comments as "conspiracy theories."

Social media has also been blamed for a dip in tourism in France, after "yellow jacket" protests by social activists were magnified in videos shared on YouTube that gave the impression the destruction was more widespread than previously believed.

“It already impacted potential customers who usually come to France,” said Diego Diaz, the head of SNCF International, France's state-owned railway service. “The violence and fires were exaggerated.”

Diaz also noted that while the protests affected tourism and train ticket cancellations, the company was also negatively affected by false claims that train travel was free for those wearing yellow jackets.

One study showed that disinformation about the yellow jackets was viewed 100 million times on Facebook alone — and that the source of the falsehoods was primarily RT, the Russian television network funded by the Kremlin.

RT videos of the protests on YouTube garnered 23 million views, more than mainstream French outlets online accounts combined, according to Avaaz, an online political activist group.

“Large multinationals are natural targets for these types of disinformation,” Diaz told NBC News, noting that SNCF is particularly concerned about the spread of fake news because it is bidding on metro contracts around the world. “When breaking news happens, it’s key to have teams and partners who monitor and address insights from social media very carefully," he said.

"Fake news today is like a modern-day tech suicide bomber in the worlds of communication, reputation and branding. It only takes one well-planned success to hurt a lot of people or an organization," said Mike Paul, president of Reputation Doctor, a public relations firm, noting that the best response involves a deep understanding of algorithms, hackers and cybersecurity along with knowledge of social and traditional media.

After hackers sent a fake post in 2013 from The Associated Press's Twitter feed saying President Barack Obama had been injured in an explosion at the White House, forcing a temporary market drop, traditional media outlets have tightened up the way they address the problems of misinformation.

“The level of sophistication used is making it more challenging," said Glenn Hall, global chief editor of Dow Jones Newswires. "We see a lot of efforts to move the market with information that is fake."

Hall relies on his own army of journalists to identify bad information sources and check for accurate website addresses, and to be on guard for videos that have been manipulated.

“It’s another thing we have to be super mindful of,” he told NBC News.

Earlier this year, some outlets, including Financial Times and CNBC.com, were duped by a letter purporting to come from Larry Fink, the chief executive of the investment firm BlackRock, who typically sends out an annual note about the company’s efforts around pro-social investing. The hoax also involved several fake BlackRock Twitter handles and a sophisticated website made to look like the company’s own.

Fake news — and urban legends such as fried rats in fast food — existed long before the internet, said David Mikkelson, co-founder of Snopes.com, a 25 year-old website aimed at debunking internet rumors.

“Twenty years ago, if you found something in a food product, what could you do about it? You complain to the neighbors or write a letter to the company, or maybe you get on the local news show. Now you post something on social media, and half an hour later it’s a headline," Mikkelson said.

“It puts companies in positions where they have to defend themselves,” Mikkelson said. “Damned if you do and damned if you don’t.”