Akamai: 10 percent of attacks directed at Telnet are directed at Port 23, which Telnet uses. Telnet is a remote access tool used to log into remote servers. Port 445, which is a commonly used port for Microsoft products, was the most targeted one. In China, attacks against SSH, which runs on Port 22, were more common than those against Port 445. Administrators are generally advised to disable Telnet if the protocol is not used to prevent attacks targeting it.”]
Source: https://www.csoonline.com/article/2126926/hackers-turn-back-the-clock-with-telnet-attacks.html