CrowdInspect is a portable tool which uses VirusTotal, Web of Trust and Team Cymru's Malware Hash Registry to reveal malware which is currently active on your network.
The program is free, extremely small (a 237KB download) and very easy to use. Download, unzip and launch CrowdInspect and it immediately identifies every process with an open network connection. A table displays the process name, ID, connection type (TCP/ UDP), local and remote ports, IP addresses and more.
Further columns display the VirusTotal and Malware Hash Registry verdict on each process. A WOT column highlights any untrustworthy domains they might be accessing, and an "Inject" column warns you if code injection has been detected for a process (which could be a sign of malware).
If you need to know more about a particular file, then CrowdInspect can display its full VirusTotal results and Windows Properties dialog. And if you believe you've spotted a problem, then there's an option to kill a particular process. But that's about it: CrowdInspect may be able to highlight some malware, but getting rid of it will require another tool.
CrowdInspect provides an easy way to check your system for malware. Keep in mind that it can only detect applications which communicate across the network, though. And it can't remove anything, either - you'll still need a good antivirus program to do that.