Shares of specialist bond insurer MBIA plunged by almost 16 per cent yesterday after ratings agency Moody's suggested that losses on mortgage securities could put the company's triple-A status at risk.

Moody's said MBIA was "somewhat likely" to reveal a capital shortfall because of the mortgage losses. The warning ratcheted up pressure on MBIA to find ways to improve its financial standing and avoid losing the top-notch credit rating that is crucial to its business model.