Today I read about Geotrust upgrading their public root certificate from 1024-bit to 2048-bit. Geotrust is upgrading the root certificate with the following reason.
This change is in line with industry best practices that GeoTrust follows to ensure the highest level of security for customers. The move to 2048-bit root keys is an industry-wide initiative. Moreover, the U.S. National Institute of Standards and Technology (NIST) recommends transitioning to 2048-bit keys.
Browser vendors have begun requiring the use of 2048-bit keys – e.g., Microsoft is requiring the upgrade for any roots that it will include in its products. Microsoft will no longer be accepting 1028-bit roots after 12/31/2010.
You can read more about the migration on the Geotrust FAQ.