Does antivirus slow transfer speeds? How to check

A file takes longer to download, upload, or copy than you expect. You might suspect your antivirus, especially if the slowdown happens during a scan. But a speed test, an internet download, and a copy between drives measure different things.

Use the Speed Test to check whether your internet connection is slow, then compare it with the transfer that feels delayed. This can help you narrow down the cause without turning off protection.

Compare speed tests and file transfers

1. Open the Speed Test and run it when your computer is behaving normally. Note the download and upload speeds, ping, and time of the test.
2. Run the test two more times under the same conditions. Keep the computer in the same place, use the same network, and pause large downloads or uploads on other devices if you can.
3. Repeat the internet transfer that seems slow, using the same file and source if possible. Note whether an antivirus scan is running, but do not download an unknown file or turn off real-time protection to create a comparison.
4. If the problem is copying files between drives, copy a large file you already trust between the same locations. Record the file size and how long the copy takes. Avoid changing ports, cables, or power settings between comparisons.

For a rough file-copy rate, divide the file size in megabytes by the number of seconds. For example, a 1,000 MB file copied in 20 seconds averages about 50 MB per second. A speed test reports megabits per second, which are different units: divide megabits per second by 8 to estimate megabytes per second, before accounting for overhead.

What the result means

The speed test is slow while antivirus activity is high

This is a clue, not proof. A scan can use processor, memory, and storage resources, and some security products inspect web traffic. Other activity on the computer or network can cause the same pattern. Repeat the comparison at a similar time with no scan running before drawing a conclusion.

The speed test is steady, but file copies slow down

Your internet connection is probably not the main cause. Antivirus software may be checking files as they are read or written, but the drive, cable, USB port, or file system can also limit copying. If only transfers involving one drive are slow, test that drive and its connection separately.

Internet transfers slow down, but local copies do not

Look at the network path first. Wi-Fi signal, router congestion, a VPN, a proxy, or the service hosting the file can affect an internet transfer without changing a local copy. A speed test measures a connection to TooLab's server, so it cannot guarantee that every other website or file service will transfer at the same rate.

Results vary from one run to the next

Small differences are normal. Speed tests use a server connection and short bursts of data, while a real file transfer may last longer and involve extra checks. Look for a repeatable change, not one unusually low result. If Wi-Fi is a possible cause, compare with an Ethernet connection using the steps in how to compare internet speeds on Wi-Fi and Ethernet.

How to reduce the slowdown safely

1. Let a scan finish. If the computer is scanning files, wait until it is done and repeat the transfer. If scans keep interrupting work, use your antivirus app's schedule to run them at a quieter time. The exact menu depends on the product.
2. Check what is using the computer. On Windows 11, press Ctrl + Shift + Esc to open Task Manager, then check the CPU, Disk, and Network columns. On macOS, open Activity Monitor from Applications › Utilities and inspect its CPU, Disk, and Network views. High activity can point to a scan or another task, but it does not identify the cause by itself.
3. Check the connection. On Windows 11, open Settings › Network & internet and check whether you are using Wi-Fi or Ethernet. On macOS, open System Settings › Network. If possible, compare Wi-Fi with a wired connection, and rerun the same test without a VPN or large background transfer.
4. Update the security app and restart. Install the latest available antivirus and operating system updates, then restart the computer. An update can fix a scanning or network-filtering problem, and a restart can clear a process that is stuck using resources.
5. Review security settings carefully. Windows 11's built-in protection is available under Settings › Privacy & security › Windows Security › Open Windows Security. Antivirus settings on macOS depend on the product you installed. Do not add broad exclusions or leave real-time protection off just to improve a transfer. If a security feature appears to be the cause, check the product's guidance or contact its support before changing it.

Why a speed test cannot settle the question

The Speed Test measures internet download and upload performance, ping, and jitter. It exchanges test data with TooLab's server. It does not measure a copy between two drives, and a good result cannot rule out slow storage or scanning of a particular file. A poor result also does not prove antivirus interference, because Wi-Fi conditions and other network traffic change over time.

For a fair comparison, keep the file, destination, network, and test conditions as consistent as you can. If the slowdown happens only with one specific transfer, check that service or drive as well as your antivirus.