I've encountered that message myself, click on a link and that stupid virus warning pops up unexpectedly. Thank you avast for blocking it. Web browers will also redflag the web address that belongs to attack site the warning originated from and alert you about the site. If it's one that isn't redflagged by the browser and you know it's an attack site then you can report it to the bowser designers and they'll check it out and put on the bad list.
