AUSTIN – Monday morning saw the second of two major guests appearing via satellite at SXSW. On Saturday, I wrote about Julian Assange’s virtual visit from London. Today, it was Edward Snowden’s turn.

The event was hosted by the American Civil Liberties Union, who beamed Snowden in from Russia. Because the connection had to be run through seven routers, he was a little hard to hear at times. But when he spoke, the auditorium full of tech developers leaned in to listen to the man who last year exposed so many of their worst fears.

Early on, Snowden was asked if mass surveillance is effective. Not surprisingly, he said no. But he did say that he understood why intelligence officials thought it was genuinely a good idea.

“No one had ever done it before – at least publicly. So they went, ‘Hey, we can spy on everyone in the world all at once, it’ll be great, we’ll know everything.’ But the reality is, when they did it, they found out it didn’t work,” he said.

Which would be one thing if, he says, one failure hadn’t led to another.

“We’ve actually had tremendous intelligence failures, because we’re monitoring the Internet. We’re monitoring everybody’s communications, instead of suspects’ communications. And that lack of focus has caused us to miss leads that we should’ve had,” he said.

Among those, Snowden says, was a tip from Russia about suspected Boston Marathon bomber Tamerlan Tsarnaev.

So, according to Snowden, this massive data mining isn’t effective. But is it dangerous?

Yes, said Christopher Soghoian. He’s with the ACLU’s Speech, Privacy, and Technology Project.

“In an NSA building, somewhere probably in Maryland, there’s a record of everyone who’s called an abortion clinic. Everyone who’s called an Alcoholics Anonymous hotline. Everyone who’s called a gay bookstore,” Soghoian said. “And they tell us, ‘Don’t worry – we’re not looking at it in that way. We’re not doing those kinds of searches.’ But I think many Americans would have good reason to not want that information to exist. … I think when you understand that the government can collect this information, at this scale, they can hang onto it and figure out uses for it down the road – I think many Americans are quite fearful of this slippery slope.”

At this point in the conversation, anyone in the crowd could be excused for drawing up plans to live off the grid. But Soghoian said that data security has actually improved of late.

“The PRISM story … put the names of billion-dollar American companies on the front page of the newspaper and associated them with bulk surveillance. And you saw the companies doing everything in their power publicly to distance themselves and also show that they were taking security seriously,” he said. “Without Ed’s disclosures, there wouldn’t have been as much pressure for these tech companies to encrypt their information. Now, there’re going to be people in this audience and there’re going to be people listening at home, who think that what Ed did is wrong. But let me be clear about one really important thing: His disclosures have improved Internet security.”

If you’d like to watch the complete conversation, it’s available on the ACLU’s website.