I played along, drawing on my experience assisting customers by phone for a computer store many years ago, acting as ignorant as I could to try to keep them hooked.
While I was on OS X, I told them I was running Windows 7. The first thing their technicians did was run me through a fake diagnostics process to see all the "junk files" and viruses I had that were slowing down my computer. They instructed me to start up my computer and run "eventvwr" (by going through the start->run process). A couple of times they asked me to tell them what I saw, and I had to google up screen shots from event viewer to feed them the right information to convince them (since I'm not actually running windows). Once they had verified that I was on board, they asked me if I could see any red or yellow warning marks after clicking on categories. They asked me to estimate the number of red marks and I told them "two thousand, three hundred".
"Oh wow, over two thousand three hundred junk files and viruses. You see sir, that is why your computer is running poorly, you are seriously infected. Let us help you clean it up". He told me every time I used email, internet, CD and DVD players, etc, that I was getting these viruses, but that their Microsoft Technicians would help me now and guarantee my computer would stay clean for 10 to 15 years.
They told me they would get their senior Microsoft Certified Technician Mr. Anderson online. Mr. Anderson (also with a thick accent) then instructed me to go to their website (quick resolve . net - check it out if you want, it's got some stock image of happy business people with a laptop and some language options, and "Get Support" buttons). They then instructed me to click the "Get Support" button and enter a code they gave me over the phone.
After entering my code, a download started. It was actually an OS X package (detected my OS) but I went along with the Windows 7 ruse, wondering if the code was specific to me (so they could see I had accessed it) and logged my access (in which case they'd be able to see I wasn't using Windows 7).. but they kept going along with it.
Anyway, they asked me to click the "run" button beside the file in the downloads list. I claimed to have trouble finding it for awhile, and then when I did "find" it, claimed I got an error box saying "User Error: User Not Retarded." They didn't seem to clue in (language barrier I guess, although their technician actually repeated the message verbatim to me), and got me to restart my computer while pressing F8 over and over (to bring up the boot options menu in Windows and try to get me to go into safe mode).
I read out that I saw "Windows Advanced Boot Options and Safe Mode, Safe Mode With Networking" and they told me to use my up and down arrows to move to "Safe Mode with Networking" and hit enter. I strung them along for a few minutes with "just wait, my mouse is not working yet." Eventually I pretended to figure it out and they had me access their download site again, with a different code this time. I once again claimed to get the "User Error: User Not Retarded" dialogue and eventually they got fed up and said they had run out of time for today but would call me back later.
I spent a half hour with them. I had nothing better to do at the time and wanted to see how it played out.