Standard & Poor's earlier this week corrected to A-plus from A the ratings on 1,096 issues guaranteed by Ambac Assurance Corp. that it had inadvertently lowered.

The agency Nov. 19 downgraded Ambac to A from AA after parent Ambac Financial Group Inc. earlier in the month reported a $2.431 billion net loss. Standard & Poor's lowered the 1,096 issues to the A level even though their underlying rating was higher.

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