"微软即时通讯软件" can be translated as "Microsoft Instant Messaging Software" or more specifically, if referring to a well-known product like the former MSN Messenger (which was later rebranded as Windows Live Messenger), you could say "MSN Messenger (formerly known as Microsoft's instant messaging software)" or simply "Windows Live Messenger" (if referring to its later iteration). However, for a general translation of the concept rather than a specific product, "Microsoft Instant Messaging Software" is appropriate.