diff --git a/bit_manipulation/count_1s_brian_kernighan_method.py b/bit_manipulation/count_1s_brian_kernighan_method.py
index d217af90b..e6d6d6534 100644
--- a/bit_manipulation/count_1s_brian_kernighan_method.py
+++ b/bit_manipulation/count_1s_brian_kernighan_method.py
@@ -1,7 +1,7 @@
 def get_1s_count(number: int) -> int:
     """
     Count the number of set bits in a 32 bit integer using Brian Kernighan's way.
-    Ref - http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
+    Ref - https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
     >>> get_1s_count(25)
     3
     >>> get_1s_count(37)
diff --git a/machine_learning/sequential_minimum_optimization.py b/machine_learning/sequential_minimum_optimization.py
index 40adca7e0..df5b03790 100644
--- a/machine_learning/sequential_minimum_optimization.py
+++ b/machine_learning/sequential_minimum_optimization.py
@@ -28,7 +28,6 @@ Usage:
 Reference:
     https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/smo-book.pdf
     https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/tr-98-14.pdf
-    https://web.cs.iastate.edu/~honavar/smo-svm.pdf
 """
 
 
diff --git a/physics/n_body_simulation.py b/physics/n_body_simulation.py
index f6efb0fec..2b701283f 100644
--- a/physics/n_body_simulation.py
+++ b/physics/n_body_simulation.py
@@ -8,7 +8,7 @@ velocity and position brought about by these forces. Softening is used to preven
 numerical divergences when a particle comes too close to another (and the force
 goes to infinity).
 (Description adapted from https://en.wikipedia.org/wiki/N-body_simulation )
-(See also https://www.shodor.org/refdesk/Resources/Algorithms/EulersMethod/ )
+(See also http://www.shodor.org/refdesk/Resources/Algorithms/EulersMethod/ )
 """
 
 
@@ -258,7 +258,7 @@ def example_1() -> BodySystem:
     Example 1: figure-8 solution to the 3-body-problem
     This example can be seen as a test of the implementation: given the right
     initial conditions, the bodies should move in a figure-8.
-    (initial conditions taken from https://www.artcompsci.org/vol_1/v1_web/node56.html)
+    (initial conditions taken from http://www.artcompsci.org/vol_1/v1_web/node56.html)
     >>> body_system = example_1()
     >>> len(body_system)
     3