That's because you are looking for the wrong thing. "No results" for what? What you search for matters.
McAfee didn't simply release a product by this name. They bought the company that had previously been making that product:
Word Mark SKYHIGH
Goods and Services IC 042. US 100 101. G & S: Computer services, namely, software as a service (SaaS) computer network services featuring software, namely, computer software for providing security for cloud computing services, with functions consisting of data security, information protection, data loss prevention, data authentication, management of security policies, monitoring cloud services usage, controlling employee access, controlling user access, monitoring and auditing cloud services, governance and auditing of public and private IT cloud services, and monitoring the security of remote computers and mobile electronic devices; SaaS services featuring computer encryption software to enable secure transmission of digital information and data; SaaS services featuring computer software to integrate managed security services, with existing communications networks, software and services; SaaS services featuring computer software for data communications applications, and for the encryption and authentication of digital information and data; SaaS services featuring computer software for authentication and identity management information security. FIRST USE: 20130430. FIRST USE IN COMMERCE: 20130430
Registration Number 4764943
International Registration Number 1171774
Registration Date June 30, 2015
Owner (REGISTRANT) Skyhigh Networks, Inc. CORPORATION DELAWARE Suite 400 900 E. Hamilton Ave. Campbell CALIFORNIA 95008
Attorney of Record Katherine M. Basile & Jason E. Garcia
Type of Mark SERVICE MARK
Register PRINCIPAL
Live/Dead Indicator LIVE
Apparently funding for the acquisition involved Morgan Stanley, who took a security interest in the "SKYHIGH" mark for computer security services, etc..
But this is Exhibit A for "why I don't believe people when they say they've 'checked the USPTO database'". Quite obviously, there is at least one registered mark for SKYHIGH in the field of computer security.