Plaintiffs in this action brought suit, individually and on behalf of all others similarly situated, against a provider of computer software programs and its corporate parent, alleging that a “plug-in” software program, created by defendants to facilitate Internet use and made available on defendants’ website for free downloading, invaded plaintiffs’ privacy by clandestinely transmitting personal information to the software provider when plaintiffs employed the plug-in program to browse the Internet. Defendants moved to compel arbitration and to stay court proceedings, arguing that plaintiffs’ claims were subject to an arbitration provision contained in license terms that plaintiffs allegedly had accepted when they downloaded the plug-in program. The United States District Court for the Southern District of New York (Alvin K. Hellerstein, J.) denied the motion. We affirm, holding that (1) plaintiffs neither received reasonable notice of the existence of the license terms nor manifested unambiguous assent to those terms before acting on the webpage’s invitation to download the plug-in program; (2) plaintiffs’ claims relating to the plug-in program are not subject to a separate arbitration agreement contained in license terms governing use of defendants’ Internet browser software; and (3) the legal doctrine that requires nonsignatories to an arbitration agreement to arbitrate when they have received a direct benefit under a contract containing the arbitration agreement does not apply to a website owner who allegedly benefited when users employing the plug-in program downloaded files from the website. Affirmed.