Users of Telegram Messengers in certain parts of the world had trouble exchanging messages through the service yesterday. The problems were caused by a distributed denial-of-service attack aiming at Telegram servers. The service outage affected users mainly in South and North America, although connection issues were present in other parts of the world as well. In a Twitter announcement, Telegram informed that its servers today were the target of a DDoS attack deployed by a network of compromised computers.
Source: Bleeping Computer