The first step is to understand how badly your system has been compromised. Often there may be a mix of issues.

Running an anti-virus software may provide some clues, as may the message you receive from your internet service provider. However if your system is compromised there is a possibility that the diagnosis you receive may also be compromised or misleading.

There are a range of web-based diagnostic applications that may also be worth checking.

If you can't get rid of the infection…

In many cases, however, it may not be possible to successfully remove all malware and return the system to a known-safe and stable configuration.

You may need to consider backing up your critical data, reformat your hard-drive and re-install a fresh version of operating system and your software.

If you feel this is beyond your abilities, seek advice from the specialists: go to the professional help page.