Mata Hari's secrets are set to be revealed, as MI5 files on spies from World War I will go online.
It will focus on history's most famous spies and the secrets in which they traded.
Hari was reportedly arrested in February 1917 in Paris before she was executed in France aged 41, the Daily Express reported.
Dr Stephen Twigge, records specialist at Kew, said that these spies disclosed the importance of the security service in safeguarding the nation during the First World War and now people across the world will be able to discover the secret history behind the war for themselves.
Other famous spies include Edith Cavell, a British nurse who assisted in rescuing the Allied soldiers but was later executed in war-torn Belgium.
Arthur Ransome, was another spy who was the author of the children's novel Swallows and Amazons and Sidney Reilly, and a Russian-born adventurer whose exploits with the British Secret Service inspired the James Bond movies.
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The database includes the interrogation reports, letters, postcards and photographs related to individuals and groups under surveillance by MI5.
Intelligence reports on major political figures such as Russian revolutionaries Leon Trotsky and Vladimir Lenin are also contained in the database.
