I'm trying to troubleshoot my sister's 2011 i5 11" MacBook Air and am looking for some advice. She reported that since Sunday, it has run very slowly, particularly while running Safari. It isn't her connection, since a Windows PC still runs fine. I have suggested resetting the PRAM and SMC, and running Disk Utility to repair Disk Permissions, all to no avail. The issue started under 10.7.2 but is still there under 10.7.3. The next step I can think of is to run the Apple Hardware Tests using Internet Recovery. Has anyone experienced anything like this? Is there any known malware that might cause this? MacKeeper comes to mind. Is there anything else? She has small children at home, so taking the Mac to the Genius Bar isn't particularly convenient, but that may be the next step. Are there any decent free diagnostics (besides AHT) that may be of help in isolating the issue?