Regex reg = new Regex(@"(?i)https?://\w+[\w+\.]+\.abc\.efg\.com");

------解决方案--------------------
修正一下
(?i)https?://\w+[\w+\.]*?\.abc\.efg\.com
C# code

Regex reg = new Regex(@"(?i)https?://\w+[\w+\.]*?\.abc\.efg\.com");