Why is this an issue?

When defining custom attributes, System.AttributeUsageAttribute must be used to indicate where the attribute can be applied. This will determine its valid locations in the code.

Noncompliant code example

using System;

namespace MyLibrary
{

   public sealed class MyAttribute :Attribute // Noncompliant
   {
      string text;

      public MyAttribute(string myText)
      {
         text = myText;
      }
      public string Text
      {
         get
         {
            return text;
         }
      }
   }
}

Compliant solution

using System;

namespace MyLibrary
{

   [AttributeUsage(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Delegate)]
   public sealed class MyAttribute :Attribute
   {
      string text;

      public MyAttribute(string myText)
      {
         text = myText;
      }
      public string Text
      {
         get
         {
            return text;
         }
      }
   }
}