The most successful software apps in the world are built with PHP. Facebook, Wikipedia, Slack, WordPress, Flickr, Yahoo. Users don't care about your tech.
PHP does have a track record of terrible security, though. WordPress and Yahoo both still have reputations as security clusterfucks; Facebook did too until they grew up as a company and were able to hire some really good security people.
However, most of the backend services at Slack (the ones you'd actually want to attack) aren't even in PHP anymore: according to their job reqs, they're in Java and Go.
However, most of the backend services at Slack (the ones you'd actually want to attack) aren't even in PHP anymore: according to their job reqs, they're in Java and Go.