I have two security programs running at the same time, can this cause conflicts?

Yeah, that’s probably a bad idea. Just stick with one. In any case, unless your browsing habits are… unhealthy, one piece of security software should have you covered nicely. Running two can cause serious slowdowns, and maybe even conflicts. Most antiviruses suffer from quirks of their own, why subject yourself to double the torture?

More is not always better. Running 2 antivirus programs at the same time doesn’t work. Don’t do it.

Windows defender alone is not enough. You could try Microsoft Security Essentials instead.

When I installed my sister’s security program it wouldn’t even let me install until I uninstalled all other similar programs

Most paid anti-virus programs slow down your computer and periodically beg for money. I would almost classify them as viruses.

I would remove McAfee and update to Microsoft Securiy Essentials (MSE), which has replaced Defender.

Mcafee can be hard to uninstall (did I mention it is virus-like?).
Here is the uninstaller:
http://service.mcafee.com/FAQDocument.aspx?id=TS100507

Also, run Malwarebytes free version occasionally, maybe once a week. It does not stay running like Defender, MSE, Mcafee, etc. So it won’t collide with your antivirus.

Malwarebytes catches different offenders than antivirus programs, that’s why I recommend it on top of your antivirus.

I have three installed and they all seem to coincide with each other. if one system does not catch a virus, one of the other two will. it has slowed my computer down a little, but i accept the slowdown, in order to have walls that protect my computer.

@john65pennington If you have one good wall, that is redundant. If you have three shitty walls then you are slowing down for no reason.

Personally I would recommend one good resident AV program (Avira is my fave) and restrict any other AV programs to periodic on-demand scans if you feel the need to run multiple AVs

jerv, thanks. i only installed three anit-virus programs, after the Trojan attack Sky Bot and totally destroyed it. it shut my computer completly down with over 800 viruses. i realize that having three may be overkill, but i am taking no more chances of losing everything and having to start over, again. thanks for your answer. john

@john65pennington I vaguely recall that. You shot your old PC and burned the remains, didn’t you?
Personally, I’ve lost more data to hardware failures and my own stupidity than to any viruses, so I stay safe by having backups of all of my important stuff. My laptop and desktop systems have copies of everything I hold dear, and the really important stuff is also archived to DVD-R, so even if a virus infects my desktop at the same time that my laptop goes tits-up, I still have my stuff!

The backup utility in Windows 7 makes that a bit easier than in previous versions of Windows as well.

yeah most likely. They each don’t like to share the same computer.