Check if a number is Prime Number or not?

Dim num1,num2 As Integer
Dim is_prime_number As Boolean
num1 = txt_number.Text

is_prime_number = True

For num2 = 2 To (num1-1)
   If num1 Mod num2 = 0 Then
       is_prime_number = False
       Exit For
   End If
Next num2

If is_prime_number Then
    MsgBox(num1 & " is a prime Number")
 Else
    MsgBox(num1 & " is not a prime Number")
End If