The antivirus software from Avast and AVG blocks security updates for Thunderbird, the developers of the email client warn on Twitter. Recently, Avast and AVG considered Mozilla Firefox to be ransomware and caused the browser to crash as a result. Problems with the antivirus software blocking Thunderbird updates have been known for quite some time. These are caused by the Mail Shield component that checks incoming and outgoing messages for malware.
In July, users already complained about the problem on the Avast forum. The forum topic in question has been viewed thousands of times. Today, the Thunderbird development team reports that the antivirus vendor is aware of the issue and has developed a beta version that provides a fix. It is not yet known when this solution will be rolled out among all users. Mozilla follower Soeren Hentzschel labels Avast and AVG antivirus software as "snake oil". He advises Windows users to take advantage of the free Windows Defender, which comes standard with Windows and costs nothing. According to Hentzschel, this virus scanner is not a "constant source of problems".