The serious delinquency rate on single-family loans guaranteed by Freddie Mac broke 3% in August, the highest reading ever.

In its monthly summary released last week, the government-sponsored enterprise said the percentage of loans 90 days or more past due and in foreclosure hit 3.13% during the month, up 18 basis points from July. In August 2008, Freddie had a 1.11% serious delinquency rate.

The huge jump in defaults was driven mainly by Freddie's $172 billion portfolio of guaranteed alternative-A loans, which had a 9.44% serious delinquency rate as of June 30. The alt-A portfolio includes $144.8 billion of interest-only loans and $11.6 billion of payment option adjustable-rate mortgages.

In August, Freddie issued $47.5 billion of mortgage-backed securities, a 7% increase from July. To date, Freddie has issued $411.2 billion of these securities, compared with $356.8 billion a year earlier.

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