How can CDS prices be above 10,000?

The reason for the question is that CDS prices are in basis points, so 10,000 basis points is 100%. CDS's insure the holder against a default on the underlying security - in Greece's case a sovereign bond. So shouldn't 10,000 basis points be the ceiling - you can't lose more than 100%, right?

No, the time until default matters too. A CDS price of 10,000 makes sense if one knows that an entity will default in 1 year and that there will be no recovery. If one knows that Greece will default on CDS in 1 month's time with no recovery, then the spread would be 120,000 basis points per year. However, the spread would only be collected for one month. So one still earns (120,000/12=) 10,000 basis points.