What is it?
syshosts.exe is a file associated with the W32.MyDoom.Y@mm worm

What does it do?
W32.MyDoom.Y@mm is a mass-mailing worm

when w32.mydoom.ymm is executed it does the following:

Copies itself as the following files:

• %System%syshosts.exe

• Note: %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
  

1. Adds the value:
   
   "MS Updates"="%System%syshosts.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that the worm is executed every time Windows starts.
2. Opens http://www.microsucks.com in Internet Explorer.

More information and removal instructions
@symantec