Security software is essential, but not all of it is built the same. Full "internet security suites" from third-party vendors often bundle a firewall, VPN, password manager, system tune-up tool, and browser extensions all in one, and every one of those components can load at startup. On an older or budget PC, this can add many seconds to boot time and keep several background processes running permanently.
Key takeaway: Windows' own built-in Microsoft Defender is a genuinely strong, lightweight alternative to bulky third-party suites, and switching to it can noticeably speed up startup.
Checking what's slowing you down
- Press Ctrl, Shift and Esc to open Task Manager, then click the Startup apps (or Startup) tab.
- Look at the "Startup impact" column — security suites frequently show as High.
- Open the Processes tab and check CPU and Memory usage during the first minute after login; a security suite's various modules (firewall, VPN helper, update checker) often appear as several separate entries.
Before you start: Never leave your PC with no active antivirus protection at all, even briefly. Always have Microsoft Defender enabled before removing a third-party product, and only run one antivirus program at a time.
Switching to Microsoft Defender
Microsoft Defender is built into Windows 10 and 11, receives regular updates automatically, and performs well in independent testing labs — without the extra background bloat of a paid suite's add-on features.
- Go to Settings > Apps > Installed apps and find your third-party antivirus product.
- Click the three dots next to it and choose Uninstall, then follow its removal wizard — many vendors include a dedicated removal tool for a fully clean uninstall.
- Restart your PC once the uninstall finishes.
- Go to Settings > Privacy & security > Windows Security > Virus & threat protection to confirm Microsoft Defender has automatically switched on.
If you'd rather keep third-party protection
Some third-party antivirus products do offer a genuinely lightweight mode. Check within the app's own settings for options to disable the VPN, password manager, or "PC tune-up" modules you don't use — each one you turn off removes a background process without reducing the actual malware protection.
Tip: If a vendor's uninstaller leaves leftover files or a stuck driver behind, search for that vendor's name plus "removal tool" — most major antivirus companies publish one specifically to clean up incomplete uninstalls.
Watching for reinstalled trial software after a reset
If your PC ever goes through a factory reset, a "refresh," or a repair install initiated through the manufacturer's recovery partition rather than official Microsoft installation media, there's a good chance the original trial antivirus suite will reappear, since manufacturer recovery images are typically built from the same factory image the PC originally shipped with. This is different from the clean Windows reinstall method described elsewhere on this site, which uses official Microsoft media and includes no manufacturer bloatware at all.
If you find yourself repeatedly clearing out the same trial suite after using a manufacturer reset option, it's a sign that a proper clean install using Microsoft's own installation media would save you the repeated effort in future, since it sidesteps the manufacturer's recovery image entirely.
Signs a leftover process is still running
Even after running both the standard uninstaller and the vendor's dedicated removal tool, it's worth double-checking for any lingering trace, since a small number of stubborn installations do slip through. Open Task Manager's Processes tab and look for anything still bearing the old antivirus vendor's name — this shouldn't normally appear after a proper removal, and if it does, it's worth running the official removal tool a second time, ideally after restarting your PC first, since some leftover services only fully release once the PC has rebooted at least once following the initial removal.
It's also worth glancing at Settings > Apps > Startup once more after the whole process, just to confirm nothing related has quietly reappeared in that list, which can occasionally happen if the removal process was interrupted partway through, such as by an unexpected restart.
Frequently asked questions
- Is Microsoft Defender good enough on its own?
- Yes, for most home users. It's tested regularly by independent labs like AV-TEST and consistently scores well against both known and new malware, all without needing a paid subscription.
- Why is my antivirus using so much CPU during startup?
- It's typically performing a full definitions update and an initial scan of recently changed files right after login, which is more intensive than its normal background behaviour.
- Can I run two antivirus programs for extra protection?
- No, this is not recommended. Two real-time antivirus engines running together often conflict with each other, causing crashes, false alarms and significantly worse performance rather than better protection.