Every time I click to open a link, other windows start opening. They all want to sell me Detox your Mac or have warnings about how my Mac is at risk or infected.
How can I check for malware?
You can check for malware and also make sure that you don't have some known adware installed:
The second link is quite long, so feel free to point out one line or a paragraph that don't make sense if you need a hand digesting it and then implementing the fixes.
I've also checked into http://www.thesafemac.com/arg/ and their product free but donation supported product Adware Medic and the program and site are valuable and honest tools for fighting malware and adware. I've chipped in some cash to help them continue to make information clear and available.
Have you installed any free programs or any open source programs? If so, they may contain adware. The website distributes its software for free, but bundles it with malicious files/adware and are payed per install. Even secure websites can sometimes acquire malware, so you should always scan whatever you download.
When you locate the free program, Google it and find out how to completely uninstall it, for some malicious files cannot be removed by deleting them, as they spread. Install some antivirus software and keep yourself protected regularly. Don't take a free program, they are very invasive.