Step 1: Run an anti-virus
You could try sending a small amount to that address and leave a public note asking them to give back your coins, they probably won't but it's worth a try.
Do not run an antivirus softwares if your computer has a high probability or is confirmed to be infected by a malware. Antivirus softwares are the first line of defense and some virus are in fact FUD (fully undetectable) by antiviruses. It is MUCH safer to get your most important files out, ensure that the virus did not infect those program and reinstall the OS.
Due to this, the best precaution is to install or run only programs that you trust and know.
The public note requires a Blockchain.info wallet and the hackers will never return your coins, no use trying.