<p>I have a class Agent with a property Id</p>

<p>Given a collection of Agents I need to check if any of them have duplicate Ids.</p>

<p>I am currently doing this with a hash table but am trying to get Linq-ified, what's a good way of doing this?</p>

```
```
foreach(var agent in Agents) {
    if(Agents.Count(a => a.ID == agent.ID) > 1)
        Console.WriteLine("Found: {0}", agent.ID);
}
```
```