The first thing I do after downloading installable programs on the web is to go to Control Panel and arrange all programs by date installed. Anything that has installed on that date, that I didn't intend to install, I immediately uninstall.
I try, carefully, to avoid those programs but some have slipped through. After the uninstall I run Malwarebytes and sometimes do a virus scan with Norton. I bought the $20/life version of Malwarebytes and run it at least once a day. I am not necessarily endorsing the purchased version and rarely buy anything when I can get a free version.
I used W8 for a short period but can't say I know,for sure, how to boot to safe mode. Of course, in W7 you can reboot and press F8 key every second or so as it starts up. You can do a forced shut down by holding the power button down. When you start back up you get the opportunity to opt for safe mode. This is not recommended.