Simda.AT is malware which infects Windows OS. It modifies hosts file contents to redirect legitimate traffic.
Simplified check for beginners
Check whether your hosts file is modified by Simda.AT
Manual check for advanced users and administrators
Open the folder "C:\Windows\System32\drivers\etc"
If you are infected, you'll find hosts.txt and hosts file with system file attribute.
Open the hosts file and go to the bottom of the file contents
If you are infected, you'll find lots of empty lines injected. Notice scrollbar on the right.
You can find injected host records at the bottom of infected hosts file contents.
Microsoft - How can I reset the Hosts file back to the default?