Jeremy Hammond, 28, who has ties to the hacking group Anonymous, admitted in May he accessed secure databases, getting personal information of thousands of people, including police officers and contractors. A federal judge imposed the maximum sentence sought by prosecutors, while Hammond's lawyers urged that he be sentenced to time served since his arrest in March 2012.
About 250 people wrote the court urging leniency, the newspaper said. One letter came from Daniel Ellsberg, who leaked the Pentagon Papers in 1971.
Hammond admitted that he hacked an Austin, Texas, company, Strategic Forecasting Inc., in late 2011. Prosecutors said credit card numbers and other information he obtained were posted online.
In 2006, Hammond received a two-year sentence for hacking into a conservative activist group. Court records showed Hammond told another hacker he had a "three-punch knockout plan" for action against police and security agents within weeks of completing parole in 2011, not realizing the person he knew as "Sabu" was working undercover for the federal government.
In addition to Strategic Forecasting, Hammond targeted the Arizona Department of Public Safety and Stratfor, a Texas private intelligence company that does work for the government and corporate clients.
Hammond's supporters say he has played an important part in revealing the shadowy world of government security contractors.
"Jeremy's actions gave us important insight into this reality that we would not have otherwise understood," Ellsberg wrote in his letter.