Niantic servers suffered severe downtime that affected all game infrastructure. The game was unavailable for several hours, much to the disappointment of the its over 10 million fans. Two hacking groups have claimed responsibility for the attack. The most plausible explanation comes with the flood of new gamers, as Pokemon Go was released in in 26 countries just before the crash. The company later announced on Twitter that it addressed the server issue. Three fake apps were found on Google Play. Two were delivering ads and scareware. A third app was locking screens of devices immediately after being installed.”]
Source: https://www.bitdefender.com/blog/hotforsecurity/pokemon-go-servers-under-ddos-attack/