Edward Snowden has come in from the cold - on Twitter.

Snowden, the fugitive former National Security Agency contractor who leaked details about the U.S. government's massive surveillance programs, started a Twitter account on Tuesday from exile in Russia with a simple handle - @snowden.

He attracted more than 171,000 followers in about an hour and had 740,000 by Tuesday evening. But Snowden himself was following only one other Twitter account - his former employer's.

"Meanwhile, a thousand people at Fort Meade just opened Twitter," Snowden said in a tweet, referring to the U.S. Army base in Maryland that is the home of the NSA.

Snowden's initial tweet was "Can you hear me now?" The message, a take-off on a cellphone provider television commercial, was retweeted 25,000 times within an hour. In his Twitter profile, Snowden described himself by saying: "I used to work for the government. Now I work for the public."

Supporters see Snowden as a whistleblower who boldly exposed government excess. But the U.S. government has filed espionage charges against him for leaking intelligence information. Snowden fled the United States in May 2013 and has been living in Russia since being granted asylum there later that year.

Initial reaction on social media to Snowden was more positive than negative. Based on a Thomson Reuters proprietary algorithm that looked at Twitter posts mentioning Snowden or his official Twitter handle, there were about 1,109 positive tweets versus 156 negative, a ratio of about 7 to 1, within the first hour of his initial tweet. The counts were from a representative sample.

In his earlier hours on Twitter, Snowden exchanged tweets with prominent astrophysicist and radio talk-show host Neil deGrasse Tyson, who had encouraged Snowden to try Twitter during an interview on his show this month.

On Twitter, the two discussed the discovery of water on Mars, and Snowden joked that his work for the Freedom of the Press Foundation keeps him busy, "but I still find time for cat pictures."

Tyson asked how he felt about being considered a traitor as well as a hero, noting that "you're a geek to me." Snowden responded that he was "just a citizen with a voice."

The user name @Snowden had already been claimed by someone who had not used it in three years. The American Civil Liberties Union, which represents Snowden, said Twitter officials were contacted and agreed to turn over the handle to Snowden.