You can check the following locations for apps that automatically launch on startup and delete any you don't need/want:
- System Preferences > Users & Groups > yourusername > Login Items (SL and older: System Preferences > Accounts > yourusername > Login Items)
- In Finder, click Go > Go to Folder > /Library/LaunchAgents
- In Finder, click Go > Go to Folder > ~/Library/LaunchAgents
- In Finder, click Go > Go to Folder > /Library/StartupItems
There may be other locations, but if you can't recall the app names, it would be tougher to locate remaining remnants.
As far as malware is concerned, Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 12 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below). 3rd party antivirus apps are not necessary to keep a Mac malware-free, as long as a user practices safe computing, as described in the following link.
Read the
What security steps should I take? section of the
Mac Virus/Malware FAQ for tips on practicing safe computing.