Similarly, if you have a site set up to make an ajax connection back to your server whenever an uncaught javascript exception happens (protip: if you do this, m

Similarly, if you have a site set up to make an ajax connection back to your server whenever an uncaught javascript exception happens (protip: if you do this, make sure to throttle it, or else if you push a bad update that makes users' browsers get stuck in a loop throwing errors, they will all try their damnedest to DDOS you!), then it's very easy for most of the reported errors to not actually originate from your site's own scripts but be from browsers broken by adware. I've been very surprised that I haven't seen more talk about this until now. I remember trying to track down a bug a few users reported, and I finally discovered that the users all had a specific piece of malware that replaced the javascript setTimeout function with a version that only took two arguments, which caused my code to break in frustratingly subtle and mystifying ways.