I came from Intego, Kaspersky, Norton, SOPHOS Pro and changed to Avast, because of its superior detection of virii.
To first of all to answer the ever re-appearing question 'I have a Mac, do I really need antivirus?': Yes, you do. It does not need to be a virus that affects OS X, you could inadvertendly cause an infection of others by you forwarding or sharing infected files. If you are in business and infect your customers, that is the sure way out of business.
I do not share the experience of any slow-downs by Avast at all. To the contrary, the use of cycles of Avast seems to be much less than other antivirus I have used over the years.
Apart from the ransomware shield and webshield, I particularly appreciate the e-mail shield of Avast, as we have been subject to a barrage of phishing and malware loaded e-mails, which all other antivirus did not detect. While I am certainly capable of identifying problematic e-mails, my associates may not. DIY also consumes precious time.
I don't share the experience of excessive invasiveness by Avast. In fact, I experience no invasiveness at all.
At the time of this writing, based on my experience, Avast antivirus is the best for Mac, in my opinion.

by Martin Brinkmann on October 31, 2014 in Security - Last Update: October 31, 2014 - 33 comments

Security companies such as AVG, Kaspersky or Avast release new versions of their products each year to the public. The updates do introduce new features from time to time and may also change the interface of the program as well.

If this happens, click Open. Step 8 The avast! Installation will begin soon, click Confirm. Program, and double-click it. Avast for mac stop notifications. Step 7 You may get a warning notification popup.

The following steps will assist you in downloading and installing Avast! Free Antivirus for Mac. If you need assistance at any point during this tutorial.
Vishnu Vardan (Avast) Hi Dancenh, We suggest you to run our AVG clear tool by referring to the article and then reinstall AVG Internet Security application and check if the issue still persists.

Avast For Mac Error Occurred Checking Definitions

Avast released its 2015 lineup recently and one of the new features that all of its antivirus programs ship with is HTTPS Scanning.

It enables the program to detect and decrypt protected traffic using its web filtering component. This alone is highly problematic considering that the program is tapping right into protected data streams but the current implementation is causing all kinds of issues on top of that.

I have a problem with any software that for whatever reason can't find and download files from the manufacturer's database. This to me is an indicator that the software is incapable of correctly installing.

Update: An update to the most recent version of Avast or Firefox seems to resolve the issue.

Firefox users for example may notice that the browser won't close anymore because of Avast's HTTPS Scanning feature. This may not happen all the time when Firefox is closed but users reported that it is happening frequently.

That's however not the only issue that Firefox users may experience if Avast is installed on the computer system the browser is running on.

Firefox's add-on update check may be blocked by the security software as well.

The Mozilla Firefox web browser is not the only program that is affected by issues though. Spotify's Web Player may not be able to connect to Spotify for example with Avast 2015 running on the system.

Users who experience issues after installing the latest version of Avast 2015 have two options:

Disable HTTPS Scanning.
Uninstall Avast completely.

It is thankfully pretty easy to disable HTTPS Scanning in the application.

Open the Avast dashboard on the affected system.
Select Settings from the left sidebar menu.
Switch to Active Protection.
Click on Customize next to Web Shield.
Uncheck the 'Enable HTTPS Scanning' option and click ok.

This turns off the feature in Avast and problems that you have experienced should be a thing of the past.

There is no option to turn off the HTTPS Scanning feature in Avast during installation. While you can disable the Web Shield during installation, it impacts more than just HTTPS scanning and is generally not recommended. (thanks Sören)

Because more and more work and life activities require personal information to be uploaded to the Internet, privacy and security is now a critical concern. Avast contains 33 number of servers and no need of login. It has consistent service which is able to connect optimal server location. Avast secure vpn license free. It is a hurdle through which users must pass through first before users can connect to their company database away from their homes.

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Avast's HTTPS Scanning interferes with Firefox and other programs

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The new HTTPS Scanning feature of Avast 2015's Web Shield interferes with programs such as Firefox or Spotify. Find out how to resolve the issues.

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Avast For Mac Error Occurred Checking Definitions