• by Gavin O'Malley  @mp_gavin, February 12, 2019

From interactive advertising to App Store optimization, today’s employers can’t get enough tech expertise.

That’s according to Upwork’s latest quarterly index of the “hottest skills” in the U.S. freelance job market.

The freelancing platform found that businesses are doubling down on their mobile efforts, which explains App Store optimization ranking fifteenth on its latest list, and app usability analysis ranking sixteenth.

Beyond mobile, companies need help realizing their full digital potential. That boosted Invision -- the digital product design platform -- to tenth place; and Intercom -- the customer messaging platform that makes apps for sales, marketing and support -- to eighth place.

The award for the hottest skill went to Hadoop -- an open source software used to store, process and analyze big data applications.

That’s because Hadoop pros are better positioned than most developers to help businesses capitalize on the value of their data, Upwork suggests.

Second only to Hadoop, productivity-focused businesses are hungry for developers with Dropbox API expertise.

As companies look to re-skill their workforces, employee training ranked eleventh on the list, while learning management solution consulting came in eighteenth.

Meanwhile, a focus on fighting cybercrime helped certified information systems security experience take the sixth spot on Upwork’s list. Likewise, OAuth -- which enables token-based authentication and authorization online and gives employees a safer and more secure way to access data -- came in thirteenth.

Upwork’s skills index calculates year-over-year growth rates based on freelancer billings.