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Don't install MacKeeper. It's known by causing problems on Macs where it's installed. See > https://discussions.apple.com/docs/DOC-3691
If you installed it, remove it > http://applehelpwriter.com/2011/09/21/how-to-uninstall-mackeeper-malware/
Please ignore it. You do not need nor want to download it. You do not need anti-malware software at the present time. See the following:
Helpful Links Regarding Malware Protection
An excellent link to read is Tom Reed's Mac Malware Guide.
Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.
See these Apple articles:
If you require anti-virus protection I recommend using ClamXav.