Suspected adware infection of Mac I have an Early 2015 MacBook Pro running OS X 10.11.6 (the latest version of El Capitan) that as of late had started randomly opening a website with the link fastlauncher.xyz [Thanks John Ramos: wouldn't be a good idea to try going to the link.] It does not happen often.  

I have tried:


to use the latest version of Malwarebytes Anti-Malware for Mac; it did not detect the adware. 
checking the browser extensions for Safari and Chrome, the two browsers I use; but do not see anything suspicious. 
checking for Login and Startup Items, nothing suspicious
restarting (I'm getting a bit desperate and maybe it'll work - it didn't)
using BitDefender (30-day trial); solved the issue


I have not tried:


using only one browser and seeing whether the adware will go away (hence I am unsure whether it is a system virus or isolated to a browser)


So far, the link has only been opened in Chrome. I would prefer manual removal over a program. Will update this list as I go.
If you suspect your Mac may have malware or adware installed on it, I would recommend trying BitDefender, a lightweight antivirus app for Mac (available for free on the Mac App Store), which I have found to be especially good at detecting both adware and malware and then removing it. BitDefender scans your machine when prompted (good for an ongoing issue) but does nothing in the background. 

If you want constant protection in the future (that promises to block malware from being downloaded onto your Mac in the first place, and has fulfilled its promise twice for me) you can try Avast, which is also free (but not available from the Mac App Store, just their website). 

Hope this helps, let me know if your problem reappears in the future.