A reporter accused police and prosecutors of a "sinister" attack on public interest journalism today as allegations she criminally obtained leaks in the phone-hacking scandal were dropped.
The Guardian's Amelia Hill said there was a "completely disproportionate response" from authorities in considering whether she and an Operation Weeting detective should face court.
The Crown Prosecution Service ruled charges were not needed after considering new legal guidelines for criminality in journalism.
But, in a statement, Ms Hill expressed anger that an investigation had taken place.
She said: "I have spent the last nine months as the focus of a criminal investigation, under the threat of prosecution.
"This was not only incredibly difficult for me personally but was a completely disproportionate response by the police and the CPS, and a sinister attempt to chill public interest journalism.
"The Milly Dowler investigation that I wrote with Nick Davies was the tipping point that forced News International to finally admit it was complicit in widespread illegal conduct.
"It led to a near £3million apology to Mr and Mrs Dowler. It also showed how the police had avoided investigating phone hacking for many years, directly leading to the resignation of three senior Met officers, including the former Metropolitan Police Commissioner, Paul Stephenson.
"The danger of these protracted police investigations is that, as in this case, the police use their criminal powers as a threat and an assault on investigative journalism. I hope the CPS's retreat today will mean that does not occur in this case."
Ten articles written by Ms Hill appeared to contain confidential details about the long-running investigation passed on from the detective, prosecutors said.
But Alison Levitt QC, the principal legal advisor to the Director of Public Prosecutions, said the information disclosed "was not highly sensitive".
"It did not expose anyone to a risk of injury or death," she said. "It did not compromise the investigation.
"And the information in question would probably have made it into the public domain by some other means, albeit at some later stage."
Guardian editor Alan Rusbridger welcomed the news, tweeting:
A spokesperson for the Guardian said: "We welcome the Crown Prosecution Service's sensible decision to abandon this worrying attempt to criminalise legitimate contact between journalists and confidential sources. Nevertheless, the paper makes no comment on the validity of the Met police assertion that the officer it identified was Amelia's source in this case."