Last weekend, the WannaCry Ransomware bit several hundred thousand computer systems, including sixteen hospitals in the UK. The ransomware infected the systems and encrypted all data. The reason this one was really bad is that it was a "worm," or a "network aware virus" that would spread out over the local area network to find other computers to infect, and bring the whole establishment to its knees.
According to Kaspersky Lab, 98% of the systems infected with this virus were running Windows 7. We were really worried about Windows XP, which was also vulnerable, and many hospitals still run Windows XP for mission critical things. Microsoft offered a patch several months ago that would have fixed this vulnerability, but hospitals have to certify and test all updates first to ensure that its equipment will continue to run as expected. There are also many cases where hardware at the hospitals are running Windows XP embedded, and can't be updated.
Read more at bleepingcomputer.com.