So I'm very content on Mavericks - I don't see much of a need to upgrade to Yosemite. But recently I have been noticing some fishy activity on my MacBook: 1) Opening my MacBook but it's starting up like I had shut down on previous use (so having to log in to my user etc), while I merely closed it on standby - it's not exactly a battery issue 2) Twice discovering a Chrome tab (amongst my 1000 tabs) on a fileshare321.com site saying I'm downloading something (even though neither Chrome nor OS X has alerted me on any downloads) I've checked my system on ClamXav and iAntiVirus, and have come clean. I also have 'Install security updates' checked under App Store in System Prefs. I am told that Apple "does not discuss their security issues", and when they released Yosemite, it's "for security purposes". So, should I definitely upgrade to Yosemite just to enhance my MacBook's security? How vulnerable is Mavericks really, seeing as Yosemite is the latest OS? Any help would be greatly appreciated. Thank you in advance!