Ever opened up task manager (windows) or top (*nix) and saw a process running that you were curious (or suspicious) about?  Me too, There are ways of finding out what it is, and it never hurts to look it up.  It could be a trojan, virus, or any other form of malware. 

The first option is simple enough, Google.  Just google the name of the executable and you'll usually find out some decent information in the first record.  Try that first. 

Second, there is Exelib.  This is a search engine exclusively for executable files.  It gives a detailed description of what the file is, but doesn't necessarily elaborate on what may be bad about it.  For instance, the svchost.exe page tells you that svchost.exe is a normal Windows executable file that it probably doing something important, but it does have a threat level of 3 out of 10.  What it doesn't tell you is what that threat might conceivably be.  I'll tell you, if svchost.exe is running as a normal user account, you've got a trojan on your hands. 

ProcessLibrary is a site similar to Exelib but its a little older.  While it may be a little older, it's also more outdated.  It doesn't list any threat whatsoever from svchost.exe.  I know from personal experience that svchost.exe is a commonly trojaned executable for Windows operating systems.

While nothing's perfect, the first place I would look for information on strange processes is Google.  Then hit up Exelib.  ProcessLibrary should be used as a last resort, its not only outdated but its inundated with ads for crap you don't want.

Another aspect to this concept is unknown file extensions.  This is very common and I run into it very often.  This website is a comprehensive resource for finding out what that weird file extension is and therefore, what you can do with it.  Superbly valuable resource.