Ok, this is driving me bananas. Since purchasing my 2012 model MBP with Mountain Lion, I've experienced CONSTANT issues relating either to a DNS Cache problem resulting in "Invalid URL" or untrusted security certificate problem -- sometimes both at the same time. I've found no shortage of mac users experiencing similar issues, but have yet to find a solution to this problem. The issues are not browser specific, and will occur at any time and on any website. Invalid URL Error: Approximately 2-3 times per week, typing "google.com" into my browser will result in an "Invalid URL" error and the only way to resolve the issue is to restart or wait approximately 20 minutes. This has happened with other common websites but Google is the most common culprit. This is not a network error as my internet connection will be perfectly fine each time it happens. Untrusted Security Certificate Probably 5-6 days per week, using Facebook, Twitter, or other common everyday websites will result in the constant security pop up warning of potential phishing, asking me to cancel or continue. If I choose 'cancel' I can rest assure I'll be prompted on every single page I open from that point forward. If I choose 'continue' I will be redirected to some gibberish website (e.g. Facebook) or an Oracle website (e.g. Twitter). I feel that both of these issues are somehow related to an internal DNS cache but so far I've had only temporary luck with the flush dns terminal command, resetting browser (including deleting all of my saved info) and/or simply restarting the laptop all together. Every time I think I've fixed it, the problem returns. I'm afraid I'm going to throw my MBP out a window next time it happens. Can anyone relate to and advise?!? So frustrating!