McAfee antivirus software can slow down some computers. Certain system resources are required to protect your computer from malicious software, and other attacks.
Automated scanning setting
McAfee making computer slow due to automatic scanning. If you don't have enough memory or have a slow processor, scanning your computer for viruses could cause problems.
Some antivirus/anti-malware programs offer an option to scan the computer only. McAfee offers active protection against threats. The application will start one or more processes that scan the computer or provide protection. The general rule of thumb is that the slower a computer runs, the more processes it has.
Full scan automatic
Since 2010, hard drive technology can't allow for a complete scan to take less than a few seconds. Each file must be checked for infection individually. It takes a lot of time and is more difficult if your hard drive is older or slower. McAfee's full scan takes the most resources, so other applications will run slower.
McAfee software may be set up to automatically upgrade, which can cause slowdowns in your computer and Internet connection. If you have a dial-up connection, your connection might be particularly slow.
Your computer may not meet the minimum system requirements to run McAfee software. Check the McAfee website for information regarding the minimum system requirements for each of their products: http://home(dot)mcafee(dot)com.
Multiple programs problem
You may encounter problems if you have multiple security software installed on the same computer. It is because the programs are not trusted and fight for permissions. You should only have one antivirus program installed at once.