Apple bought at least 3 companies in the past year that nobody knows about

Apple buys so many companies, there are some purchases it has made that have never been revealed.

Parsing CEO Tim Cook's recent statements, it looks like there are 3 buys that have never been reported.

"We've made 15 acquisitions in the last four quarters to accelerate our product and services roadmaps, and we're always on the lookout for companies with great technology, talent, and strategic fit," CEO Tim Cook said on a conference call to discuss Apple's earnings call earlier this month.

Then he doubled down during an appearance on CNBC. "We generally acquire a company every three to four weeks on average. And so it's a rare month that there's not a company being bought," Cook said.

Since March 28, 2015 - four quarters ago - here's all the companies we know Apple has bought:

1. FoundationDB, a company that made database technology for web applications
2. LinX, an Israel-based camera company whose tech could end up in this year's iPhone
3. Coherent Navigation, a company that worked on high-precision GPS
4. Metaio, a German augmented-reality company
5. Mapsense, a California company that made tools for location data
6. VocalIQ, a British company that made machine learning software for speech recognition
7. Perceptio, a startup using deep learning technology to identify images
8. FaceShift, a Swiss company that made technology for generating facial animations with a computer
9. LegbaCore, a two-person security firm
10. Emollient, a California-based artificial intelligence startup
11. LearnSprout, a San Francisco company that made a data dashboard for educators
12. Flyby Media, a augmented-reality startup

So that leaves three blank spaces. The actual number could be higher: some Apple purchases are reported months after they close, so some of these 12 reported companies might fall out of Cook's one-year timeline.

Cook has hinted that he's willing to buy billion-dollar companies, and Apple continues to be on the prowl for additional acquisitions.

As Apple likes to say, it buys smaller technology companies from time to time - but as it turns out, it's actually all the time.

Know a company Apple bought that's still under wraps? Email the author at kleswing@businessinsider.com.