I have about 20 years of computer experience, and am pretty familiar with Anti-Virus software. The one thing that you DON'T want to do if something like this happens is turn off your AV program, because you will be putting your system at serious risk if it is a real threat, and most of the time, they are. Avast's false-positives are very rare.
1.) Instead, contact your Anti-Virus company through e-mail or by submitting the link to the Virus Lab that you found at your Anti-Virus company's website. (Use hxxp: instead of http for the format of the suspected link so the link is not accidental clicked on in the e-mail.) The describe the problem to your Anti-Virus company in the e-mail message.
2.) If you get a bad file in a download, create a zip folder and place the folder temporarily on your desktop.
2. a.) Move the suspected file to the zipped folder. (Don't doube click the file!)
b.) Password protect the zipped folder by double clicking on the zipped folder (not the file in the folder!)
c.) On the File Menu, click "Add a Password"
d.) In the password box, type a password
e. In the Confirm Password box, type the password again.
3.) Attach the file in to your e-mail message. In the subject line, write "Please investigate this potential virus file."
4.) Describe the issue you had in the body of the e-mail message. Put the password in the body of the e-mail message.
5.) Submit to your anti-virus company for testing. If it's a false-positive, a definition should be out within 12-24 hours for the next update. If it is a virus, because it is getting blocked after 1-2 AV updates from the time you sent the file or URL, you know a real infection has been blocked.
6.) After submission of the file, delete the zipped folder from wherever you put it and empty your Recycle Bin.
6.) If you have, or can get to the e-mail of the site without going to the site during the time the threat is being investigated, make sure to report that your AV picked up a virus, so that the webmaster can investigate.
But NEVER EVER turn off your Anti-Virus if a threat has been detected! That's the worst thing you can do! The proper thing to do is to scan the site with virus total,
www.virustotal.com, which provides scans for about 40 different anti-virus scanners. Wait until virustotal.com shows that the site is clean, than you can visit it again.
Satch