This link from McAfee will assist you with any virus or malware issues you may have. Please be sure to follow the recommendations in the link and run the McAfee Stinger scan which is included in the link.
No antivirus software from any software vendor can guarantee 100 percent that one would never contract virus or malware but I can just imagine what issues you may have had in the past if you didnt have any protection in the first place.
Have you tried to run the McAfee Virtual Technician found at the top of this page under Useful Links in the Techical Support Link? MVT will scan your computer for any McAfee related issues and if it finds any it will attempt to resolve them. You could also chat with Tech Support after MVT is finished running for further help.
Are you up to date with all Windows updates and IE8 ? It is very important to keep updated so to prevent issues from occurring, but sometimes they occur anyway. I do not recommend any use of registry booster or registry cleaner programs as they often do more harm than good.
Your scan log that informs you that a trojan was found should have told you what the trojan was and when it found it and has quarantined in from infecting your computer.
I hope some of this information is helpful to you