National Security Agency (NSA) director Alexander was the latest, and perhaps the most controversial, federal official to attend the annual hacker conference in Las Vegas to recruit warriors for battles being fought on the Internet.
"I am absolutely impressed with some of the stuff going on here," Alexander said during a keynote presentation to a packed auditorium.
"In this room is the talent our nation needs to secure cyber space."
His Def Con visit came after he was quoted by the New York Times as saying that between 2009 and 2011 there was a 17-fold increase in cyber attacks on critical US infrastructure such as power grids and mobile phone networks.
Along with being boss of the NSA, Alexander is an Army general and head of US Cyber Command created to defend against Internet-based attacks.
"My concern is destructive attacks with serious consequences on critical infrastructure (and key government systems)," Alexander said.
He displayed a list of major companies including banks; credit card firms; videogame and car makers, and even computer security outfits, successfully hacked in the past two years.
"There are a lot of companies with tremendous cyber security expertise getting hacked," Alexander said.
"The reality is that this is the community that who builds many of these tools," he continued with an apparent reference to software weapons wielded by cyber attackers.
"This community, better than anyone, understands where this is going and what we can do to fix that."
He referred to Def Con as "the world's best cyber community."
Alexander, who sprinkled humor and personal stories into his talk, displayed a website for NSA job seekers.
"We need great talent," he said. "We don't pay as high as some of the others, but we are fun to be around."
Reaction in the audience ranged from stone-faced silence to grumbling that if federal official want hackers to be their friends they should stop arresting them.
"Some will go for it and some won't," one hacker said of the potential for peers to be one over to Alexander's cause.
Alexander did not take questions directly from the audience but did answer queries that Def Con founder and organizer Jeff Moss, whose hacker name is Dark Tangent, received via Twitter or other channels.
First, Moss said, he wanted to know whether the NSA keeps files on everyone and, if so, how he could see his.
Moss has gone on to head security at the agency responsible for the world's website addresses since starting Def Con as a young hacker 20 years ago.
"Absolutely not," Alexander said, noting that the humorous question deserved a serious answer. "The people who are saying we are doing that should know better."
Alexander held firm that the Internet defenses could be ramped up without sacrificing privacy or civil liberties. A "perfectly secure" Internet is in the nation's best interest and would help revive the staggering economy, he argued.
"Look at all the intellectual property we've lost over the past decade," Alexander said. "It's huge. If we could fix that it would help our economic growth."