i have avast 7 free installed on my computer. if i insert a pendrive (with a virus) all the folders appears as shortcut. i know that its a virus doing it. but if i scan the pendrive using avast, it does not detect the virus. what should i do?
send all the suspect infected files to avast via www.avast.com/contact-form.php
next,follow this guide: http://forum.avast.com/index.php?topic=53253.0
attach all logs here…
remember,no antivirus can 100% of everything every AV misses something.
@Sathish1995
Hello and welcome to avast. 
Step#1
Download MCShield from one of the following links:
MyCity - Official download link
Softpedija - Mirror download link
[*] Double click MCShield-Setup to install the application.
[*] Wait a few seconds to MCShield finish initial scan.
Recommendation to under General and Scanner tab you click on Defaults button to choose recommended options.
[*] Connect your USB storage devices to the computer one at a time. Scanning will be done automatically.
When all scanning is done, you need to attach a logreport that has made MCShield.
Start → All Programs → MCShield → Logs
Attach here → AllScans.txt
Explanation: USB storage devices are all the USB devices that get their own partition letter at connecting to the PC,
e.g. flash drives (thumb/pen drives, USB sticks), external HDDs, MP3/MP4 players, digital cameras,
memory cards (SD cards, Sony Memory Stick, MultiMedia Cards etc.), some mobile phones, some GPS navigation devices etc.
Step#2
Download DDS and save it to your Desktop from here:
http://download.bleepingcomputer.com/sUBs/dds.scr
Double click dds to run the tool.
* When done, DDS will open two (2) logs:
1. DDS.txt
2. Attach.txt
Save both reports to your desktop. DDS.txt and Attach.txt attach back to topic.