Brainteaser III

The Ominous

Come get Some......
Secret Agent
To code his message, the Agent began by writing three words - each word being a number, e.g. FIVE. In doing this, he did not write any single letter of the alphabet more than once. For each of the letters thus written, he then substituted a digit and, in doing so, he used each of the digits 0 to 9 inclusive once (and once only).
He now had three numbers (all in figures) each of which was a perfect square. By adding these numbers together, he obtained a total running to five figures. IN place of the digits in this total he now wrote the letters for which each of them had originally been substituted. This gave the letters NONSO. What were the three perfect squares - in figures?