Apple unveiled an update version of mobile iOS at its Worldwide Developer Conference Monday, revealing a set of new features for its in-house iMessage app, but at least one technology firm founder is not happy about it.

Jan Koum, founder and chief executive of WhatsApp, took to Twitter to express his disappointment at Apple, whose new iMessage allows users to send audio and video files, share their locations, start and leave group chats and send messages that self-destruct a few moments after sending.

Most of these features are already available in WhatsApp, a cross-platform messenger app that has around 500 million users from around the world and is available for iOS, Android, Windows Phone and BlackBerry. WhatsApp was further propelled into stardom in February when Facebook decided to buy the startup messaging app for a massive $19 billion price.

"Very flattering to see Apple 'borrow' numerous WhatsApp features into iMessage in iOS 8," writes Koum on his Twitter account. Apparently, more than 2,000 of his followers agree. Just 12 hours after Koum posted his angry tweet, 1,500 people re-tweeted his post and more than 500 followers favorited it.

very flattering to see Apple "borrow" numerous WhatsApp features into iMessage in iOS 8 #innovation

— jan koum (@jankoum) June 2, 2014

The new iMessage also takes a page from popular ephemeral messaging app Snapchat and now allows users to set an expiration time on their messages, billing the feature as a way to save disk space on their smartphones, but many already believe the new feature takes aim at Snapchat, which currently owns the self-destructing messages domain. Unlike WhatsApp, however, Snapchat's response was not as inflammatory.

"It's exciting to see other companies begin to embrace deletion by default," says a Snapchat representative in a statement.

iMessage is not the only new threat to other companies. Apple also pulled the wraps off its iCloud Drive, a file storage system not unlike Microsoft's OneDrive, which took its cue from other cloud storage services such as Box and Dropbox. iCloud Drive, as Apple announced, allows users to automatically send backups of photos from the phone straight to the cloud drive, taking a jab at Dropbox's photo organization tool Carousel, which was announced earlier this year.

"Apple taking open approach to cloud storage! Huge move," says Box chief executive Aaron Levie on Twitter. Dropbox representatives declined to comment.

Apple also announced Handoff, a syncing feature that allows users to start writing a message on their iPhones and finish the text in another device. Handoff also works in other iOS apps, including Pages, Keynotes, Numbers, Mail, Reminders, Calendars and Safari.