I was browsing and a security alert popped up saying my iMac has been blocked due to a virus that will steal all my private info, it went on to say to call apple at a provided phone number before proceeding I
backed out not trusting what I was reading
iMac (27-inch Mid 2011), OS X Yosemite (10.10.3)
Any such popup message will be a scam, do not interact with such messages.
Yes, that's a scam. The number, if called will cost you a lot of money!, either that or the scammers will convince you to let them access your computer so they can install all kinds of nasties.
Although this is quite unlikely, if you have the time, I'd recommend you checking that your Mac isn't infected with any ad-injection Malware (aka adware).
Force quit Safari, then restart Safari while holding the Shift key
I agree completely with stedman1; Force quit Safari, then restart Safari while holding the Shift key. that should be enough.
Then in Safari menu "clear history and website data".
backed out not trusting what I was reading
Then you do not need to do anything else.
Read Phony "tech support" / "ransomware" popups and web pages.
virus alert
