How has the powerful Stuxnet malware evolved to affect several firms in the utility sector?

The Stuxnet malware had hit the headlines for its devastating attack on the Iranian uranium enrichment centrifuges. The sophisticated worm was first identified by the infosec community in 2010, although it was in the development stages since at least 2005. The malware is believed to have been created by US and Israeli intelligence agencies. Stuxnet is designed to alter Programmable Logic Controllers (PLCs) used in the types of industrial control systems (ICS). The PLCs are commonly used in facilities such as power plants, water treatment facilities, gas pipelines, etc. The worm mainly relies on multiple previously known zero-day exploits to infect computers.