Avast is on deal right now on Windows Deals. Figured Id let everyone know: http://www.windowsdeal.com/w/avast-internet-security-2015-discount-coupon-code/
DO NOT DOWNLOAD, you get a text file containing the following: "Avast Internet Security 2015 (100% Discount) No license is required. During installation, select 30 days trial and finish. You will get an extension to 180 days (6 month) Note: Free updates for 6 month are included, but NO tech support WindowsDeal.com" And the 2nd download link they provide to the Avast installer, doesn't match checksums with the current official installer: https://i.imgur.com/laLdtbv.png Just download it from the official Avast website - http://files.avast.com/iavs9x/avast_internet_security_setup_online.exe
Just a guess but the automatic extension to 6 months may be the reason why checksums are different. Avast normally offers a 30 day trial AFAIK.
Perhaps... they did used to offer an extension after the 30 day trial if you decided to switch to the free version rather than upgrade, I don't remember how long it was. However, I highly doubt Avast would distribute a modified version for offer sites, or allow these sites to distribute their own modified version. They'd keep it simple with a license IMO.
If you switch to free version the license is for 1 year. I have seen several vendors offering different installers for promos, sometimes hosted from their own sites and sometimes from intermediary platforms. I'm not exactly sure in this case though.
