diff --git a/µBlock-and-others:-Blocking-ads,-trackers,-malwares.md b/µBlock-and-others:-Blocking-ads,-trackers,-malwares.md
index 6e38cd7..c4571bc 100644
--- a/µBlock-and-others:-Blocking-ads,-trackers,-malwares.md
+++ b/µBlock-and-others:-Blocking-ads,-trackers,-malwares.md
@@ -10,6 +10,9 @@ Measuring directly the number of distinct 3rd-party domains which were hit is a
 
 ![Privacy benchmark graph](https://raw.githubusercontent.com/gorhill/uBlock/master/doc/img/privacy-benchmark.png)
 
+Caveat: "3rd-party" is defined as a domain which doesn't match the domain of the web page. For sure many 
+domains reported as "3rd-party" actually belong to the same entity which owns the page domain (for example, `yimg.com` is owned by `yahoo.com`). There is no way for the benchmark code to know this, unless using a comprehensive database of who owns which domain -- that is beyond my means. Still, the benchmark is useful if comparing blockers among themselves, or against when no blocker is used.
+
 Results -- figures are "**3rd party** / all". Ordered from least 3rd-party hits to most 3rd-party hits. Privacy-wise, lower numbers are better.
 
 #### µBlock 0.2.1.1