Recently I’ve come across a strange situation: Mozilla applications (Firefox, Thunderbird) stopped resolving hostnames. Connecting to servers using their IP addresses worked fine, but when I used a DNS name – the application gave me the finger :( Other programs worked flawlessly. After a lot of digging, I’ve found the culprit – the Kaspersky Internet Security suite.
The whole issue could have been funny if it weren’t for the time wasted resolving it. The first thing I did after learning about the problem was… turn off protection in Kaspersky. That didn’t help, so I’ve rejected the idea that Kaspersky might be the cause of the trouble. An hour of searching later I’ve stumbled upon this article from Mozilla’s knowledge base. And what did I learn? That despite turning off protection, Kaspersky might still prevent programs from accessing the net. Oh-Em-Gee. Why? Because as a result of updating any application, KIS might stop recognizing it and start treating it as one not allowed to communicate. Hello? The last time I checked it was year 2011 and automatic updates were not cutting edge anymore, but rather a standard. To cut it short, Kaspersky is done for me :) You cannot offer a product which is supposed to make users safer and in practice, even after alleged disabling, it makes it impossible for them to use consciously installed (and previously working!) applications.
To end positively, using the instructions from the above mentioned document enabled me to quickly restore proper name resolving in both applications.