I'm s server-side developer and used to invoke the `nc` command to check whether a remote port is open.

Suddenly, the security guy prohibited the command and as soon as I use the `nc` command my accessibility to the EC instance get lost.

They're saying

> 
> Use `telnet`.
> 
> 
> 

My questions are

* Is the `nc` command dangerous?
* Has any security hole?
* Has any functionality can be used in any dangerous way?