The website for Trump Tower, Donald Trump's glitzy signature skyscraper in Manhattan, went offline for about an hour on Friday after activist hacking group Anonymous denounced the real-estate mogul and Republican presidential front-runner for his anti-Muslim comments.

The website for 68-story Trump Tower, which Trump often uses for his presidential campaign, was down after Anonymous announced on Twitter: 'Trump Towers NY site taken down as statement against racism and hatred. http://www.trumptowerny.com/(what you see is cloudflare offline backup).'

Earlier this week, the group posted a video on YouTube with a message that read: 'Donald Trump think twice before you speak anything. You have been warned Mr. Donald Trump.'

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Hacked: Donald Trump was the target of an attack by the activist group Anonymous on Friday

Hit him where it hurts: The group took the website of Trump Towers in new York City offline for an hour

Declaration: They announced on Twitter that this was done as a statement against 'racism' and 'hatred' over his anti-Muslim comments

The group's warning to Trump came days after the outspoken billionaire proposed to temporarily bar Muslims from entering the United States in response to last week's shooting spree in San Bernardino by two Muslims who the FBI said had been radicalized.

A recent poll by New York Times/CBS News showed Americans are more fearful about the likelihood of another terrorist attack than at any other time since the weeks after Sept 11, 2001.

A gnawing sense of dread has helped lift Trump to a new high among Republicans who will vote in primaries to choose their party's nominee for the November 2016 presidential election.

Anonymous, a loose-knit international network of activist hackers, or 'hacktivists,' is famous for launching cyber attacks on groups such as the Islamic State following the attacks in Paris last month that killed 129 people.