An Austrian museum took down five Gustav Klimt paintings on Friday and put them into storage after receiving e-mails that they would be destroyed.
Portrait of Adele Bloch-Bauer I was painted in 1907
The e-mails said this was to stop them being taken out of the country.
On Monday a court ordered Austria to return the five paintings to the heir of a Jewish family that fled the country during the Nazi era.
Police said later on Friday that they had arrested a 50-year-old man who said he sent the e-mail while drunk.
Interior Ministry spokesman Rudolf Gollia said the man had been tracked down through his internet provider.
Mrs Altmann's family originally owned the paintings
" Now that the immediate threat for the paintings has been eliminated, it is up to the museum to decide whether the paintings will be exhibited again," he said.
The move to take the paintings down was recommended by the Interior Ministry, the Belvedere Museum said.
The Austrian government has not yet commented on the decision for the paintings to be returned to Maria Altmann, who had been locked in a legal battle with them since 1998.
But a lawyer for Mrs Altmann told the BBC the ruling was binding and final.
The paintings are worth at least $100m (£59.6m) and Ms Altmann's family, major shareholders in an Austrian sugar refinery before World War II, had their savings plundered from a Swiss bank by the Nazis.
Art Nouveau master Klimt is one of Austria's most celebrated painters.
The paintings include one of his most famous works, a portrait of Mrs Altmann's aunt, Adele Bloch-Bauer.