The following code appears in Houdini 6's zoek_smp.cpp. Translating to English, this loop goes through each of the active threads and sums up the total nodes searched. Before returning that value, however, the value is increased by knopen / 7.

uint64_t ThreadPool::bezochte_knopen()
{
	uint64_t knopen = 0;
	for (int i = 0; i < activeThreadCount; ++i)
		knopen += threads[i]->rootStelling->bezochte_knopen();
	knopen += knopen / 7;
	return knopen;
}

Due to how integer arithmetic works on a CPU, given any N, it can be shown that if you let X = N + N/7, then X % 8 != 7. This repository proves that the version of Houdini that has participated in the Division Premier of TCEC seasons 13, 14, 15, and 16, contains the above code.

The file parse.py reads the PGN files from each DivP of TCEC seasons 13, 14, 15, and 16, and collects the node counts that Houdini outputs. That data is found in output.txt and I encourage you to reproduce my results. If we then take all the node values N, and generate a histogram of N % 8, the following is the result:

0: 1746, 1: 1741, 2: 1725, 3: 1704, 4: 1652, 5: 1687, 6: 1733, 7: 0

This histogram provides damning proof that Houdini's output for nodes searched is modified like the code above. The code above appears in Houdini 6's source files.

I believe that Houdini is a direct clone of Stockfish, and is in violation of the GPL.