My iMac has been getting slower and slower. Today, it took almost 10 minutes to sign in and check email, and to open Excel to do a 30 second update to a spreadsheet. Even logging into Mac Forums took a couple of minutes before I could enter anything into a field. I am running OS 10.9.2. Is there something I should be running to clean up/defragment/check for malware/etc, to get my iMac back to its usual speed?