The Silicon Valley leaders looked past their day-to-day rivalries to express support for Cook, who on Wednesday announced Apple would not develop software enabling the FBI to hack into the iPhone of one the two terrorists behind December's killings in San Bernardino, California. The FBI has asked Apple to build a so-called back door to penetrate the cellphone's password protection with the hope of retrieving data related to the attack that killed 14 people. Both terrorists also were killed.
Google CEO Sundar Pichai was one of the first bigwigs to side with Cook.
WhatsApp cofounder Jan Koum also came out on Wednesday against the FBI's request.
Twitter CEO Jack Dorsey, who also heads the Square mobile payment system, on Thursday joined the bandwagon against unlocking the attacker's cellphone.
Facebook issued a statement saying the company will "continue to fight aggressively against requirements for companies to weaken the security of their systems," but didn't specifically refer to the contretemps between Apple and the feds.
The debate even lured John McAfee, a pioneer of computer antivirus programs. He volunteered on Thursday to hack into the iPhone for the FBI to avoid a situation in which the government obtains or develops back-door technology.
Silicon Valley and telecommunications companies came under fire for their security standards after former National Security Agency contractor Edward Snowden leaked materials revealing that federal agencies monitored Americans' phone records and Internet use.
Since then, Apple and Google have engineered their devices so the companies can't unlock them, even when ordered to do so.
Reform Government Surveillance, an umbrella organization representing AOL (which owns The Huffington Post), Apple, Dropbox, Evernote, Facebook Google, Linkedin, Microsoft, Twitter and Yahoo, cautiously rebuked the federal government in a statement on Wednesday.
"Reform Government Surveillance companies believe it is extremely important to deter terrorists and criminals and to help law enforcement by processing legal orders for information in order to keep us all safe," the statement said. "But technology companies should not be required to build in backdoors to the technologies that keep their users’ information secure. RGS companies remain committed to providing law enforcement with the help it needs while protecting the security of their customers and their customers’ information."