diff --git a/data/category-ads b/data/category-ads
index 0a4ab630..8d2584b7 100644
--- a/data/category-ads
+++ b/data/category-ads
@@ -1,4 +1,5 @@
-# This file contains domains that clearly serving ads
+# This file contains domains that clearly serving for ads or tracking.
+# We can not seperate ads and tracking domains clearly, so they are mixed together.
 include:category-ads-ir
 
 include:36kr @ads
@@ -79,7 +80,6 @@ ads.huan.tv
 ads.huantest.com
 ads.trafficjunky.net
 ads.wteam.xyz
-adservice.sigmob.cn
 adtechus.com
 adtrue.com
 adxprtz.com
diff --git a/data/category-ads-all b/data/category-ads-all
index 1723c344..bcd1779c 100644
--- a/data/category-ads-all
+++ b/data/category-ads-all
@@ -1,4 +1,5 @@
-# This file contains domains of all ads providers, including both the domains that serves ads, and the domains of providers themselves.
+# This file contains domains of all ads/tracking providers,
+# including both the domains that serves ads/tracking, and the domains of providers themselves.
 include:category-ads
 
 include:addthis
@@ -29,6 +30,7 @@ lijit.com @ads
 mfadsrvr.com @ads
 mgid.com @ads
 ns1p.net @ads
+sigmob.cn @ads
 sigmob.com @ads
 spotxchange.com @ads
 unimhk.com @ads