Why it matters: The heads of WhatsApp and parent company Meta have opened another round of verbal jousting over who has the best and most secure messaging service. Like before, the main flashpoints are cloud backup security and cross-platform interoperability.

This week's new advertisement for WhatsApp is the latest jab at Apple for refusing to extend encrypted messaging and other features to non-Apple platforms. On social media, Mark Zuckerberg and WhatsApp boss Will Cathcart contrasted the app's latest features with iMessage.

An ad above the entrance to Pennsylvania Station shows three message bubbles in different colors. One is green to represent SMS or MMS messages appearing on iPhones, and one is blue to represent iMessage. A third is white and labeled "Private Bubble" to characterize WhatsApp and its privacy features. The ad implies that iMessage's restriction to iPhones makes it less secure than WhatsApp.

Apple's messaging service features end-to-end encryption when all users in a conversation use Apple devices. However, iPhones revert to unencrypted SMS or MMS texting with Android phones. On Instagram and Twitter, Zuckerberg and Cathcart mentioned WhatsApp's end-to-end encryption, which extends to cross-platform conversations.

Google criticized Apple's policy earlier this year, encouraging the company to allow RCS messaging on iPhone. Google adopted RCS on Android last year, which also encrypts end-to-end. The company has since complained that Apple locks users into its ecosystem by only allowing encryption and other advanced features through iMessage.

During its court battle with Apple last year, Epic Games pointed out that Apple wouldn't bring iMessage to Android because it would simply encourage iPhone-owning parents to buy their kids Android phones. During a Vox panel last month, Apple CEO Tim Cook explicitly said he'd rather convert users to iPhones than allow RCS messages between iPhone and Android users.

Zuckerberg and Cathcart also highlighted WhatsApp's end-to-end encrypted cloud backups. The pair said Apple doesn't support this feature, but it's a bit more complicated.

Apple encrypts iCloud iMessage backups but also retains keys to those backups. That policy makes it easier for users to recover their messages if they lose their passwords but gives Apple an encryption key to their messages. Cathcart tweeted that Apple can't open encrypted WhatsApp backups on iCloud but didn't say whether WhatsApp or Meta can.

WhatsApp has also recently taken flak from a competitor over security concerns. Earlier this month, Telegram founder Pavel Durov used a WhatsApp security advisory from last month to call the service fundamentally insecure. He referred to WhatsApp's vulnerabilities as "planted backdoors" and called the app a surveillance tool.