Prosecutors had sought an 18-month prison term for Park Dae-Sung, 30 -- better known by his Internet alias "Minerva" -- while some media freedom groups criticised the decision to charge him.

Park was arrested in early January and charged with spreading online rumours that the government in late December ordered local banks not to buy dollars as part of efforts to stabilise the won.

Prosecutors claimed the December posting led to dollar hoarding, forcing the government hurriedly to inject two billion dollars to stabilise the currency market.

"Considering all the circumstances, it is hard to conclude that Park was aware the information was misleading when he wrote the postings," said Judge Yoo Young-Hyun of Seoul Central District Court.

The judge said that even if Park had realised the information was false, it cannot be concluded he intended to damage the public interest, considering the circumstances at the time or the special characteristics of the foreign exchange market.

Park wrote more than 200 economic commentaries in recent months and gained a major following after correctly predicting the collapse of US investment bank Lehman Brothers last September.