USPS.gov Website Infected with Blackhole EK

**Executive Summary:** A United States Postal Service RIBBS site (ribbs.usps.gov) was compromised and used to deliver the Blackhole exploit kit via an encoded JavaScript iframe and a staged redirect to a malicious page disguised as a 404 error. The attack performs browser and OS fingerprinting to select appropriate exploits and served multiple payloads (EXE, JAR, PDF, PHP) with low antivirus detection rates; the intermediate malicious redirect domain was later taken offline.