README.md: SIM must not perform IMSI detach
diff --git a/README.md b/README.md
index 1d032e4..edbde8a 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,11 @@
Kc. The applet triggers a refresh, which causes the SIM to do a new Location
Update with the new IMSI.
+It is important, that the SIM does not invoke the IMSI detach procedure (TS
+04.08 Section 4.3.4). This is controlled by the network. Otherwise it becomes
+trivial to correlate the detach of the old IMSI with the attach or Location
+Update of the new IMSI.
+
## Notes
### What if the SMS gets lost?