Why I have to do an on-demand scan on downloaded files and CDs

[TAP]

Hi all,

This may be a stupidest question here, you know this suggestion has around when you read the expert's suggestion about how to protect ourselves from viruses.

Please correct me if I'm worng, the following suggestions I took from KAV 5 Help file.

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Rule 2: be careful when copying any new data to your computer:

- Always scan all removable drives (floppy disks, CD-ROM drives, flash cards, etc.) for viruses before using them.

- Be careful with e-mail messages. Never open e-mail attachments, even if it was sent to you by a person your know, unless you have been expecting it. In particular, do not trust e-mails that claim to be sent by anti-virus companies.

- If you download an executable file from the Internet or from a LAN, scan it with Kaspersky Anti-Virus Personal.

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What I'm wondered is that why I have to do an on-demand scan on downloaded files and CDs before I open them. What I understand is all files that get in and out my computer are automatically scanned by AV's real-time scanner. If files have a virus and AV's real-time scanner cannot detect a virus on-the-fly but when I open/run files or extract archive files then an AV's real-time scanner will detect and block a virus suddenly if it's a known virus. So do I need to scan on downloaded files and CDs before I open them?

Please correct me if I'm worng.

Thanks.

[controler]

No you don't have to do on on demand scan of them when you download them but lets say you have some files sitting around for a month or two that you downloaded from kazza and one or more are infected. I would think a full drive scan would be helpful if your antivirus now has the DEF's to catch it but did not before.

controler

[bigc73542]

In a perfect world your av should scan them as they are downloaded. But since this is not a perfect world I would do a manual scan of all downloaded fifes/folders programs etc. There are some real nasty baddies out there you do not want on your computer.

[Arin]

dear TAP, thats a good question. why don't you join the forum? ok here is the answer. typically its true that On-Demand scan is not needed as the On-Access scanner always scans files before they are loaded into the memory. but in real world scenario things are slightly different. these are the important factors why an On-Demand scanner should also be used atleast once a month.

1. some AVs have different settings for On-Demand and On-Access scanners. the default settings of On-Access scanners are optimized for both protection and performance. OTOH On-Demand scanners are tweaked for protection only.

2. some viruses targets the On-Access scanner so that you'll be lured into a false sense of security.

3. generally archives or bulky files are excluded from On-Access scans but included by default in On-Demand scans.

4. files skipped or undetected by On-Access scanner are checked by On-Demand scanner.

well it doesn't mean you're unsafe if you don't use the On-Demand scanner. its just that running the On-Demand scanner makes you safer.

[Blackcat]

-{ Quote: "these are the important factors why an On-Demand scanner should also be used at least once a month and include

1. some AVs have different settings for On-Demand and On-Access scanners. the default settings of On-Access scanners are optimized for both protection and performance. OTOH On-Demand scanners are tweaked for protection only.

Well it doesn't mean you're unsafe if you don't use the On-Demand scanner. its just that running the On-Demand scanner makes you safer." }-

Good overall answer, Amrx particularly this first point. DEFAULT settings on some AV programs are set as a compromise between protection and performance.

Dr Web for example has it's SpiderGuard, their running Monitor, set up out of the box with their smart scan setting which is very light on system resources but it does not check files when executed. But try running this AV on the FULL setting, checking files that are created, executed or opened, your machine grinds to a halt!

With NOD, the best settings for AMON, are again hotly discussed;

http://www.wilderssecurity.com/showthread.php?t=14015&highlight=AMON+setting

http://www.wilderssecurity.com/showthread.php?t=16658&highlight=AMON+setting

http://www.wilderssecurity.com/showthread.php?t=37509

http://www.wilderssecurity.com/showthread.php?t=33204&highlight=AMON+setting

In contrast some AV's default settings on their running guards are very heavy e.g. AVK Pro, RAV and you have to change these settings to achieve adequate performance on your system. These heavy settings may be optimised towards protection, as I think, these default parameters are used in testing with the Virus Bulletin.

Overall, regular scanning with your on-demand scanner on FULL settings is essential to check for any malware which have passed through the net of your on-access monitor.

[solarpowered candle]

It is good practice to save to desktop and >right click> scan with anti virus before loading any downloaded software for the first time . Most anti virus only take minute to check .(even Kav lol )

[TAP]

Thanks for all responses.