My favourite Windows defrag program is MyDefrag, which is amazing at improving program startup and access times, especially on older computers.
However, it doesn't defrag some system files, and I found that Smart Defrag can do this at boot time if you ask it to, so I occasionally use this program.
Today I ran it to do that very thing, and after a minute or so the program disappeared, and I saw a notice telling me I'd been automatically upgraded to version 3. I clicked the OK button and then saw lots of other things appearing.
It had installed Advance System Care, A Browser Toolbar, changed my default search engine to Yahoo (with a spigot referrer), installed several Spigot Programs, and 3 browser plugins for Ebay, Amazon and DNS lookup failure redirect!
I uninstalled the programs, reset the settings, ran Malwarebytes on the system and it found several other things in the temp folder, including one it reckoned was a Fake antivirus program. These all had date and time of when I'd run Smart Defrag.
Curious now, I did the same on another computer that also had Smart Defrag version 2 installed, and lo, after a minute or so it quit and presented me with the screen shown in the attachment.
I now realise I hadn't noticed the tick boxes the first time around, and so had agreed to have all that junk installed on my computer at the same time. I think this is really sneaky, I'm usually pretty good at noticing things like this, but I hadn't asked for the update, it just went ahead with it.
I unticked the boxes and let the installation of SmartDefrag 3 complete.
When it had done so, I looked at my installed programs, and found that despite unticking the options, SmartDefrag had also installed Spigot Search Protection. It had also left a file in the temp folder that MalwareBytes says is a Fake Anti Virus application (file called Resource_AcceptRate.exe)
My search engine in IE and Chrome has also been changed to Yahoo, with a referall to Spigot. The start page has been similarly changed.
These things happened on the 2nd PC despite unticking all the options presented to me in the screen shown in the attachment
So, given the way this is forced on you, my advice would be to avoid SmartDefrag and uninstall it if you're using it.