Adding to the underground feel of Facebook was the viral spread of the site.

Facebook给人以地铁的感觉，也是因为网站的快速传播。

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The product is free to use for individuals, and we've seen a lot of viral spread among sales colleagues.

个人用户可以免费使用这款产品，而且我们已经看到，它正在销售人员中以极快的速度大量普及。

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Last Fall Facebook put the hammer down, and let publishers know that the viral spread of games via notifications was going away.

但现在事情起了变化。去年秋天，Facebook就告知发行商其将禁止通过“通知”功能推广游戏。

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The viral spread of MP3-swapping software such as Napster is changing the way students consume music.

CNN: Music sites turn college students into street marketers

But a Pentagon spokesman acknowledged the already-leaked documents' viral spread across the internet made it unlikely they could ever be quashed.

BBC: Pentagon demands Wikileaks return Afghanistan documents

As the Supreme Court prepares for its second day of oral arguments concerning same-sex marriage, gay rights supporters are flocking to a viral image being spread by Human Rights Campaign: its logo.

FORBES: Behold the Same Sex Marriage Solidarity Meme