Police in the North say a suspected bomb found at the venue for a PSNI recruitment event was a "viable device".
It was initially thought the device discovered at the Waterfoot Hotel was an elaborate hoax.
The hotel had been due to host one of three PSNI recruitment events today.
However, the Derry event has been deferred until next Saturday.
Two others which were also subject to security alerts in Belfast and Omagh are going ahead.