Avast

Key technologies Antivirus and anti-spyware engine
avast! Intelligent Scanner
Silent/Gaming Mode
Behavior Shield
Real time anti-rootkit protection
Smart virus updates
avast! Community IQ
Behavioral Honeypots
Green computing
avast! iTrack
File System / Mail Shield
Web Shield
IM / P2P Shield
Network Shield

Antivirus and anti-spyware engine
State of the art scanning engine provides reliable protection against viruses, spyware and other forms of malicious software.

Real time anti-rootkit protection
Unique "on access" technology checks all kernel-mode drivers that the operating system is loading for signs of rootkit behavior. This enables even unknown rootkits to be detected and stopped before they can do any damage.

avast! Community IQ
Most samples we process come from sensors deployed throughout the avast! community in the Behavior shield and anti-rootkit modules. This is a unique source of data made possible only thanks to our huge user base. Most of the collected samples are analysed by a number of automated processes and only a small fraction of the samples need to be processed manually by our virus analysts.

Code emulator
When a suspicious executable is encountered (during both on-demand and on-access scanning), avast! is able to emulate the program’s code in an isolated environment. The code emulator is used for two purposes. First, it is used for generic unpacking. Secondly, it is used in the heuristics engine. Technically, this is done using dynamic translation, a method much FASTER than traditional emulation techniques.

Download Link:
setup_av_free.exe

Note: U can use the full Version from there official site.