I called the number listed. It connected me to an outfit called IntelliGeeks, people with heavy Indian accents supposedly in Hawaii. I foolishly gave them access to my computer and told me that there was malware on it and that my personal information was at grave risk. They wanted me to give them $299 to fix it.
I declined and called Apple today. They said that the things IntelliGeeks said showed that my computer was compromised were normal and that there was nothing wrong with my computer security. Checking into them online, I ran into several people who reported that they're scam artists who install malware themselves. Several people at Yahoo said that they'd them fix non-existent problems. The consensus is that they're scam artists.
If you ever run into IntelliGeeks, run in the opposite direction.