I let someone convince me that IE's security problems were a thing of the past and went back to using it (it was also sorta-kinda a condition for employment) and I ended up getting a few drive-bys from ads. I remember one of them was AV 2009, another might have been Conficker. I went back to Firefox with the NoScript and AdBlock add-ons, haven't had a drive-by since, and am never going back to IE. The amusing thing was that Vista's UAC let the malware right in without ever raising a fuss, but denied me access when I tried to delete them. I had to delete the virus from a Linux OS that I had on a bootable CD.
Then there's the animation rig I paid a guy to build for me. I had built machines myself before, but didn't want to spend the time to research the various components this time. I also figured this guy had more market savvy than I did. Well, the guy delivered the machine six months late, but that was the least of it. He bought and installed the wrong CPU, purchased a bootleg copy of Windows off eBay without realizing it, got a hard drive off eBay that was marked as new but was used enough that it started squealing after a day of use, and didn't notice that the motherboard's RAM slots were faulty and caused worsening memory errors to crash the machine after about 48 hours of operation. All these things were issues that I had to diagnose, discover, and correct; he was oblivious to all of it. He accused me of trying to scam him, refused to refund me for the CPU, promised to refund me for the OS and hard drive, but disappeared before doing so.
Then there's the animation rig I paid a guy to build for me. I had built machines myself before, but didn't want to spend the time to research the various components this time. I also figured this guy had more market savvy than I did. Well, the guy delivered the machine six months late, but that was the least of it. He bought and installed the wrong CPU, purchased a bootleg copy of Windows off eBay without realizing it, got a hard drive off eBay that was marked as new but was used enough that it started squealing after a day of use, and didn't notice that the motherboard's RAM slots were faulty and caused worsening memory errors to crash the machine after about 48 hours of operation. All these things were issues that I had to diagnose, discover, and correct; he was oblivious to all of it. He accused me of trying to scam him, refused to refund me for the CPU, promised to refund me for the OS and hard drive, but disappeared before doing so.