Avast is inserting advertising in my e-mail signature - how do I stop it?

I upgraded Avast the other day and now a signature line advertising Avast is appearing in my e-mails sent from Gmail. How do I stop this from happening? The offending content is not visible in the field to edit my signature in GMail or even in the draft e-mails before I hit send. This is seriously not okay and I was given no warning that with the upgrade I would suddenly be forced to advertise Avast to my contacts. I tried disabling the Firefox extension but it hasn’t fixed the problem. I tried writing to Avast using their contact form but it requires an order ID, which I don’t have (I am using the free product and first downloaded it a few years ago). Please tell me how to stop this insertion of content in my own messages without my consent.

(And if anyone from Avast is actually reading this, wtf?! You’re about to lose a user over this - just when I was seriously considering getting a paid version of your product. EDITING E-MAIL I SEND without getting my prior consent to do so or even showing your added content in the message until after it’s sent is SERIOUSLY skeezy.)

OK, I am an idiot and somehow did not find this when initially searching Avast Support. http://www.getavast.net/support/remove-e-mail-signature

Avast, I still contend that inserting content in someone’s e-mail as an opt-out function rather than an opt-in, especially when inserting that content in such a way that the person may send many messages (as I did) without even realizing that anything is being appended, is really not okay and makes me question whether I should keep using your product.

The option to have avast add a message to a mail has been there for many years.
That option hasn’t changed in the latest version.

It is a good practice that if you want to use software to learn what it does, what settings/options it has etc.

You give your consent when you install the software and use the default settings.
You can disable it very easily into Mail settings. Anyway, if you trust a security company to scan your email, why an appended message will change anything regarding to security?

This was very helpful - worked perfectly! The Avast helpdesk person did not know about the signature and hung up on me. Thank you Forum!!!

I would suggest your first port of call if you have an issue is the avast support forums.

Here you generally get a fast response, mostly from other knowledgeable avast users (on occasion avast staff) we don’t hang up and we don’t charge.