The information comes from a new form of analysis conducted by Germany's 16 state police services and the Federal Criminal Police Office (BKA).
The security services used the Radar-ITE system for their analysis, which was developed by the BKA and Swiss scientists. The system analyzes the "dangerous" individuals according to 73 characteristics, including familial surroundings, job security and propensity to violence.
At the same time, the security services concluded that the other half of those classified as dangerous pose a high risk.
The German police and intelligence agencies use the word Gefährder (risk person) to describe Islamists who they believe have the potential to carry out acts of terror.
The analysis has so far focused on the Gefährder who are currently living freely in Germany. Many others are serving prison sentences or have travelled abroad, often to Syria.
The BKA hopes that the system can help Germany's overstretched police services to focus on the people most likely to pose a terror threat. It is also intended to provide Germany's first consistent means of classifying radical Islamists across state boundaries.
Germany was hit by several terror attacks in 2016, the most serious of which was an Isis-linked truck rampage at a Berlin Christmas market a year ago on Tuesday. Anis Amri, a young Tunisian man, hijacked a truck and drove it into a crowded market, killing 12 people and injuring dozens more.
German authorities were heavily criticized in a subsequent investigation for failing to deport Amri, who was at one point considered the most dangerous Islamist in Berlin.
Interior Minister Thomas de Maizière has said that the security services have foiled three terror attacks this year. According to the SZ, 50 “dangerous” Islamists have been deported so far in 2017.
The German Police Union (GdP) believes that a completely secure surveillance system for Islamist extremists is impossible to achieve.
“For one thing intrusions into the personal space of individuals is strictly controlled by the law. Secondly the police need around 24 officers for a round-the-clock observation. We simply have neither the capacity to do this nor the legal capability,” said GdP chairman Oliver Malchow on Monday in an interview with the Heilbronner Stimme.