Explain the concept of using the 'sealed' keyword in programming and its purpose.

The keyword sealed in C# is used to restrict inheritance of classes or overriding of methods.

• For classes: sealed prevents other classes from inheriting from this class. This is useful when you want to prevent further extension of a class, for example, for security or optimization.

• For methods: in combination with override, sealed prevents further overriding of the method in derived classes.

Example:

public class BaseClass {
    public virtual void Method() { }
}

public sealed class SealedClass : BaseClass {
    public sealed override void Method() { }
}

// Attempting to inherit from SealedClass will cause a compile-time error
// class DerivedClass : SealedClass { } // Error

// Attempting to override Method in a class inheriting from SealedClass is also impossible

Using sealed helps control the architecture of the application and prevents unwanted changes in class behavior.