Can you run two antivirus programs at the same time?
The short answer
Two full real-time antivirus engines, no. They fight over files, slow the PC down and can even miss threats. Malwarebytes is the one exception by design. It is built to run alongside your main antivirus, including Microsoft Defender.
In detail
Real-time scanners hook deep into the system and inspect every file the moment it is touched. With two of them, everything gets checked twice. Each scan triggers the other scanner. Their quarantines clash and the system slows to a crawl. Windows knows this. When you install a third-party suite, Microsoft Defender switches to passive mode by itself.
Malwarebytes is the exception. It was built on purpose as a second layer. It registers itself in a way that lets it work with your main antivirus instead of competing. Defender plus Malwarebytes Premium is a popular and sound combination. Defender covers the broad baseline. Malwarebytes adds a specialist for the newest threats and unwanted programs.
One real-time engine plus scanners you run by hand is always fine. The free version of Malwarebytes works exactly like that. Use it as a second-opinion scanner and cleanup tool when you think something slipped through. More real-time engines bring conflicts rather than extra protection.
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