Head of the Linux Mint project confirms there was a window of opportunity for you to have downloaded a compromised .iso yesterday:
http://blog.linuxmint.com/?p=2994
http://www.neowin.net/news/linux-mint-website-hacked-malicious-iso-offered-on-saturday
http://blog.linuxmint.com/?p=2994
http://www.neowin.net/news/linux-mint-website-hacked-malicious-iso-offered-on-saturday