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The Russian Twitter bots are back. Or more accurately, they never left.

After Wednesday's mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, thousands of tweets poured in using the hashtag #guncontrolnow and jumped on the trending topic #Parklandshooting. These weren't coming from Americans with thoughts on the country's gun-rights debate. They were from Russian-controlled bots jumping on this divisive issue.

Among the most tweeted two words from the Russian bots were "gun control" and "school shooting," according to Botcheck.me, a tracking website that follows 1,500 propaganda bots on Twitter.

Sound familiar? The way the bots seized on this issue and played both sides is eerily familiar with how they have taken control of debates ranging from Black Lives Matter to the 2016 US presidential election. It's a strategy direct from the Russian trolling playbook: Jump on a hot button issue and stir outrage on both sides of the argument. The continued resurgence of bot influence underscores the difficulty that tech giants like Twitter, Facebook and Google face in fighting propaganda -- even after they've identified the problem.

Despite the grilling these companies have received since the 2016 election, the bot influence didn't end. And it didn't end Friday, with the US government's indictment of the Internet Research Agency, a Russian troll factory that's spread chaos across social media. The Alliance for Securing Democracy, which tracks Russian bots on Twitter, has created a website called Hamilton 68 to follow the propaganda in real time.

Before the school shooting, the bot army had been tweeting about US special counsel Robert Mueller but then quickly stormed both sides of the gun control debate once the news broke, according to the New York Times. The Internet Research Agency did the same before the 2016 election, such as setting up both pro-Trump and anti-Trump rallies using Facebook.

It's happening again

Congress members generally consider Russian bots a threat to US democracy, and intelligence agency leaders warn that Russians are seeking a repeat attack during the 2018 elections. But Sen. Jim Risch, a Republican from Indiana, downplayed the propaganda campaign's effects. During a Senate Intelligence Committee hearing last Tuesday, Risch said that Americans wouldn't fall for these bots again.

"I think that now, they're going to look askance a lot more at information that is attempted to be passed out through social media," Risch said. "The American people are smart people, they realize that there's an attempt to manipulate them, both domestically and foreign."

But last week, the gun-related tweets escaped skepticism and were believable enough to pop up on Twitter's trending topics, hijacking popular hashtags to muddy the debate.

Over the last few months, Twitter and Facebook have vowed to fix these issues, with Facebook CEO Mark Zuckerberg making it his new year's resolution. And in a blog post last month, Twitter acknowledged that 1.4 million people were exposed to Russian propaganda on its social network and said it's focused on preventing bot accounts from surfacing.

The social network said it blocks 523,000 bots a day on Twitter.

Yet somehow, thousands of bots still thrive on the platform and managed to pounce on the Florida school shooting.

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