Complex sentence: The threat level was raised from limited to substantial in April 2007 when NCTb has revealed that the Netherlands has been specifically mentioned in international terrorists' websites, and that the country has 2,500 to 3,000 potential Islamic radicals.
Split into simpler sentences: The threat level was raised from limited to substantial in April 2007. The NCTb has revealed that the Netherlands has been specifically mentioned in international terrorists' websites, and that the country has 2,500 to 3,000 potential Islamic radicals.