lol looks like you got your self a trojan xd
it's fake scanning software, you don't really have any where near the amount of viruses that it may claim
While there are no viruses for Mac OS in the wild, there are trojans - malware that masquerades as some useful software and tricks you into granting permission for it to install. Once you have given permission to OSX for a program to install or run, all security bets are off.
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If your Google serches are being hijacked to pages at cool-book, this is a trojan called DNSChanger. The malware installed when you downloaded something from the web, sometimes masquerading as a video codec or other useful software.
DNSChanger removal tool
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Clam (open source antivirus)
Mac
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In terms of cleaning up your machine, OSX does much of that for you with daily, weekly and monthly automatic maintenance that runs overnight.
You can use a program called Onyx to clean up caches, and to trigger the maintenance scripts.
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One thing you can do is to go to Disk Utility and run a "Repair Permissions"
Then, you can boot from your OSX DVD, and launch Disk Utility from the Utilities menu, and do a "Repair Disk" which will correct errors in your hard drive catalogs and files.
In order to speed up booting and performance in general, reduce the number of things that automatically start, or that run in the background. Reduce the number of Dashboard widgets and browser plug ins that you have loaded.
Macs are so much easier, and faster. One prick decided to make one of the 0.01% of viruses that work on Macs.
Actually Ubuntu/linux is the fastest when it comes to OS
not too mention it's free.