This is only true if you have the original file to compare the altered file against. It is possible to determine a file has been altered but it now much more difficult to do so. M/L algorithms on known file types should be able to discover these modifications, identifying that there is probably a needle in this haystack, but as the paper explains it is harder to detect the presence of a secret and the secret is still protected even if you find it.
Odd_Mathematician_80 t1_jbedvjh wrote
Reply to comment by volci in A group of researchers has achieved a breakthrough in secure communications by developing an algorithm that conceals sensitive information so effectively that it is impossible to detect that anything has been hidden by thebelsnickle1991
This is only true if you have the original file to compare the altered file against. It is possible to determine a file has been altered but it now much more difficult to do so. M/L algorithms on known file types should be able to discover these modifications, identifying that there is probably a needle in this haystack, but as the paper explains it is harder to detect the presence of a secret and the secret is still protected even if you find it.