@thegibson - in 2002/3 ish I was performing a security assessment of a bank when they insisted I perform the internal Nessus scan during business hours. 30 seconds after the scan started their AIX server crashed taking all business with it. Noticed I had accidentally clicked “enable dangerous plugins” in Nessus.
@thegibson - about a year after that I was testing an ISP’s out of band management network when I noticed a flood of ICMP TTL expired fly across my tcpdump window. (Always recorded all my tests)
A second later their two largest, most powerful, routers crashed due to a routing loop.
The worst part was before I started I confirmed with the network team there were no routing loops because I wanted to be more aggressive with scanning.