Czechoslovak secret police collaborator 
In October 1998, the newspaper Süddeutsche Zeitung accused Helmut Zilk of having collaborated with Czechoslovak secret police (StB) during the 1960s. He denied the accusations. Based on this and also on information from the StB archives, Zilk was denied of a planned Czech medal of honor and the affair was widely covered by Czech and Austrian media. In 1998 Czech presidential office cleared Zilk and president Havel did apologize to him in person.
In 2009, the StB documents on Zilk were made public. These documents record 58 meetings between Zilk and secret police agents during 1965–68. Zilk had provided information about the political situation in Austria and assessment of individual Austrian politicians; for this he was paid in money and goods like Bohemian crystal glass. After the Soviet occupation of Czechoslovakia (August 1968) Ladislav Bittman, one of the agents in contact with Zilk, defected to the West and leaked information about him. Some Czech media (as well as the old StB documents) speculated that the continued political and journalistic career of Zilk, in spite of being uncovered, was due to some other agency (CIA is suggested) recruiting and supporting him.
- Heinrich, Mark (2008-10-24). "Ex-Vienna mayor targeted by letter bomb dies at 81". Reuters. Retrieved 2008-10-26.
-  Briefly:Havel Apologizes on Spy Charge
- "Photocopies of some StB documents about Helmut Zilk (23 pages)" (in Czech). MF Dnes. Retrieved 2009-03-12.
- "Helmut Zilk may have worked for StB and CIA" (in Czech). MF Dnes. 13 March 2009. Retrieved 2009-03-13.
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