I recently downloaded a new version of Adobe Flash Player or possibly Adobe Reader. Imagine my surprise when the Adobe Download Manager reports that in addition to installing Flash, it also installed McAfee Security Scan Plus. At the time I assumed that perhaps this was done only to secure the download process and didn't think much of it. At the time I did not see an option to not select this software, but it may have been there.
It turns out that this is security scanning software from McAfee. And while it is legitimate software, it only scans for threats and does not prevent or remove them. On their web page it is promoted as a "Free Download" and it "Actively checks your computer for anti-virus software, firewall protection, and web security, and threats in your open applications."
On the same page is a large link for "McAfee Virus Removal Services". Described as "McAfee Virus Removal Service detects and eliminates viruses, Trojans, spyware and other malware from your PC easily and quickly in the comfort of your home" for the low low price of $89.95.
So we'll try to lure you in with free software. In this case Adobe is complicit. And then after we find some sort of issue we will try to get $89.95 out of you because you don't know any better.
Needless to say, I've removed this software because I already have antivirus software running on my computer. There is an option to uninstall in the Programs menu.
I will be more diligent when downloading from Adobe in the future.