Sorry for the inconvenience. A few days ago someone pointed a network of a couple thousand zombie computers at this site. I found a way to effectively block them from disrupting the use of the site, but increasing security also resulted in a small number of legit users being blocked. Also, if your computer is infected with malware then the security filter may think you're a bot and not a person.
I previously asked the mods to keep an eye out for members complaining that they have to answer a question to prove they aren't a bot before they can get to this site so that I can whitelist their ip to keep that from happening to them. This is the first I've heard that it had happened to anyone.
From wikipedia:
Zombies can be used to conduct distributed denial-of-service attacks, a term which refers to the orchestrated flooding of target websites by large numbers of computers at once. The large number of Internet users making simultaneous requests of a website's server are intended to result in crashing and the prevention of legitimate users from accessing the site. A variant of this type of flooding is known as distributed degradation-of-service. Committed by "pulsing" zombies, distributed degradation-of-service is the moderated and periodical flooding of websites, done with the intent of slowing down rather than crashing a victim site. The effectiveness of this tactic springs from the fact that intense flooding can be quickly detected and remedied, but pulsing zombie attacks and the resulting slow-down in website access can go unnoticed for months and even years.