Avast! 4.8 Professional Edition

While Avast may not be especially thorough, it is fast

PC World (US online)

Specifications:

Contacts
Website
www.avast.com
Software Version
Version
4.8
System Requirements
Minimum System Requirements
Windows 95/98/Me: 486 Processor, 32MB RAM and 100MB of free hard disk space. Windows NT 4.0: 486 Processor, 24MB RAM and 100MB of free hard disk space and Service Pack 3 (or higher) installed Windows 2000/XP Workstation (Not Server): Pentium class Processor, 64MB RAM (128MB recommended) and 100MB of free hard disk space Windows XP 64-bit Edition: An AMD Athlon64, Opteron or Intel EM64T-enabled Pentium 4 / Xeon processor, 128MB RAM (256MB recommended) and 100MB of free hard disk space Windows Vista, Windows 7: Pentium 4 processor, 512MB RAM and 100MB of free hard disk space Windows Vista 64-bit Edition: An AMD Athlon64, Opteron or Intel EM64T-enabled Pentium 4 / Xeon processor, 128MB RAM (256MB recommended) and 100MB of free hard disk space
*Specifications are subject to change without notice. While every attempt has been made by IDG Communications in the production of these specifications, possible errors or omissions may still occur. IDG Communications neither assumes legal liability or responsibility for the accuracy, completeness or usefulness of any product specifications supplied.