Complex sentence: He also contributed to the National Strategy to Secure Cyberspace, and later served in the National Cyber Security Division of the US Department of Homeland Security where he proposed the creation of the US-CERT in 2003.
Split into simpler sentences: He also contributed to the National Strategy to Secure Cyberspace, and later served in the National Cyber Security Division of the US Department of Homeland Security. He is credited for proposing the creation of the US-CERT in 2003.