diff --git a/module3/exo1/influenza-like-illness-analysis.ipynb b/module3/exo1/influenza-like-illness-analysis.ipynb
index cc5b6b8ea553e413f2505d7ab0cfe49aa05321cb..027c79e2df39bf23d4ced98982e188d54c6bdde5 100644
--- a/module3/exo1/influenza-like-illness-analysis.ipynb
+++ b/module3/exo1/influenza-like-illness-analysis.ipynb
@@ -57,6 +57,13 @@
     "The first line of the CSV file is a comment, which we ignore with `skip=1`."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "It is preferable to first make a copy of the data, and then use that copy in the computational document. To ensure traceability of the data, the computational document must nevertheless contain the URL from which the data was obtained (which we have above). A reader can then download the data again and compare with the version used in the analysis. When publishing a computational document, the copy of the data is published as well, after verifying that republishing the data is legally possible. Below we make the local file with the data if it doesn't yet exist."
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 5,