As Middle East regimes try to stifle dissent by censoring the Internet, the U.S. faces an uncomfortable reality: American companies provide much of the technology used to block websites.

McAfee Inc., acquired last month by Intel Corp., has provided content-filtering software used by Internet-service providers in Bahrain, Saudi Arabia and Kuwait, according to interviews with buyers and a regional reseller. Blue Coat Systems Inc. of Sunnyvale, Calif., has sold hardware and technology in Bahrain, the United Arab Emirates and...