Belgium has not accused the U.S. of any wrongdoing.
Like other EU leaders, Di Rupo has expressed anger over reports of U.S. electronic espionage overseas and said the Obama administration should agree by year's end to stop alleged American eavesdropping on foreign leaders, businesses and law-abiding citizens.
Last week, Finland, another European Union nation, said its computer networks had been widely hacked but said no highly sensitive information was lost.
Since the discovery in Di Rupo's office, the Belgian government has improved and sped up its cybersecurity strategy, committing 10 million euros ($13.5 million) annually to counter any spying or computer hacking.
Di Rupo also now asks government ministers to leave their mobile phones outside his office during sensitive meetings there.
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Follow Raf Casert on Twitter at http://www.twitter.com/rcasert