A system for providing security in a computer system, the system comprising: a plurality of ring oscillators (1021 - 1024) that are identical as designed but have different oscillation frequencies as manufactured, the plurality of ring oscillators (1021 - 1024) being equipped with a respective plurality of counters configured to count impulses of oscillating outputs of the plurality of ring oscillators (1021 - 1024); and one or more logic circuits configured to at least: start the respective plurality of counters, and stop the respective plurality of counters, over repeated counting periods; select a group of ring oscillators from the plurality of ring oscillators (1021 - 1024), the group of ring oscillators being equipped with a respective group of counters of the respective plurality of counters; the system being characterised in that the logic circuit is configured to determine a correlation between oscillating outputs of the group of ring oscillators based on counter values obtained from the respective group of counters over the repeated counting periods, the counter values indicating oscillation frequencies of respective ring oscillators of the group of ring oscillators; and generate a notification indicating interference in the group of ring oscillators and thereby the plurality of ring oscillators (1021 - 1024) when the correlation is above a predefined threshold correlation. a plurality of ring oscillators (1021 - 1024) that are identical as designed but have different oscillation frequencies as manufactured, the plurality of ring oscillators (1021 - 1024) being equipped with a respective plurality of counters configured to count impulses of oscillating outputs of the plurality of ring oscillators (1021 - 1024); and one or more logic circuits configured to at least: start the respective plurality of counters, and stop the respective plurality of counters, over repeated counting periods; select a group of ring oscillators from the plurality of ring oscillators (1021 - 1024), the group of ring oscillators being equipped with a respective group of counters of the respective plurality of counters; the system being characterised in that the logic circuit is configured to determine a correlation between oscillating outputs of the group of ring oscillators based on counter values obtained from the respective group of counters over the repeated counting periods, the counter values indicating oscillation frequencies of respective ring oscillators of the group of ring oscillators; and generate a notification indicating interference in the group of ring oscillators and thereby the plurality of ring oscillators (1021 - 1024) when the correlation is above a predefined threshold correlation. start the respective plurality of counters, and stop the respective plurality of counters, over repeated counting periods; select a group of ring oscillators from the plurality of ring oscillators (1021 - 1024), the group of ring oscillators being equipped with a respective group of counters of the respective plurality of counters; the system being characterised in that the logic circuit is configured to determine a correlation between oscillating outputs of the group of ring oscillators based on counter values obtained from the respective group of counters over the repeated counting periods, the counter values indicating oscillation frequencies of respective ring oscillators of the group of ring oscillators; and generate a notification indicating interference in the group of ring oscillators and thereby the plurality of ring oscillators (1021 - 1024) when the correlation is above a predefined threshold correlation.