Does avg slow down your computer?

I must disagree with David. I have been in the computer sales and service field for over 25 years and must say that I have found Avast to be one of the worst antivirus programs on the market, surpassed only by AVG in its ineptitude. The programs that I recommend and sell to my clients at this point is Kaspersky Antivirus.

To answer your question directly, yes, Avast can slow down your machine as it can be set up incorrectly to do more scans than are necessary. Just like what Norton Antivirus allowed people to do about a decade ago (which is what soured people against their software), Avast can be set to scan files each time they are accessed, created, edited, deleted, or closed or some combination of these various file operations. Some people feel that having the software scan files at all stages of file operation is advisable and necessary. Doing so means that it can bring a machine to a crawl. In the most extreme example, I once saw a client's machine take over half an hour just to boot to the desktop. Most antivirus programs do not allow access to those options precisely for this reason. Instead, they allow the configuration of what should be scanned (Smart Scan (it selects the appropriate files to scan), Extension List (it scans files based on a certain configurable list of extensions), or user-configurable (the user gets to set whatever he wishes to have scanned).

Also, Avast can slow down your machine indirectly because of the multitude of infections that it fails to detect. It is not uncommon for me to have a machine come in that is allegedly protected by Avast and the user is complaining about the machine not working correctly or running slowly and when I scan it with Kaspersky, I find up to 3000 infections that were missed. Once those are removed, even if Avast is left on the machine, the machine works worlds better, though after showing easily that Avast is inferior, most clients ask me to put on Kaspersky, after which they do not have problems anymore.

If you are looking for an antivirus that is better than Avast and do not wish to pay for a commercial product, then I recommend Avira. You can get their free product at http://www.avira.com/en/avira-free-antivirus I have recommended and used them for certain clients over the years and while it is not as good as a commercial product (you get what you pay for, after all), it is definitely the best of the freebies.

If you have any other questions or need further advice, feel free to drop me a line.