Sunday, April 15, 2007

Bypassing Your Browser's Cache

As your browse the web, your browser frequently stores many parts of a web page (content, images, javascript etc.) into a so-called "cache" located in your computer's hard drive. This is done with the belief that certain parts of a web page won't change much, for example a company's logo.

But because of this, you might find that sometimes your browser refuses to download the latest data from a web site but instead uses the outdated data stored in its cache. Refreshing might help, but certain elements of a web page may still be retrieved from the cache.

When this happens, you have to be hard on your browser by forcing it to do a "hard refresh", i.e. bypassing your browser's cache entirely. Listed below are the ways to do this for different browsers.

Internet Explorer

either: Hold the Control key, and press F5.
or: Hold the Control key, and click the Refresh button on the toolbar.

Firefox, Netscape (versions 6.x and 7.x) and SeaMonkey.

either: Hold down the Control key, and press F5. On an Apple Mac, use the Command key instead of Control.
or: Hold down the Control key, and click the Reload button on the navigation toolbar.


either: Hold down the Command and Shift keys, and press R.
or: Hold down the Shift key and click the Reload toolbar button.

Opera doesn't have an option to do a hard refresh, so if a normal refresh does not seem to work, you'll have to clear the cache by going to 'Tools' > 'Delete private data'. Click 'Details', make sure that 'Delete entire cache' is selected, and then choose any other data you want to remove.

Friday, April 13, 2007

Scan a File With Multiple Antivirus Engines

What do you do when you come across a suspicious file that you think contains a virus but your antivirus software gives a negative result? Or when you got a seemingly safe file from a trusted source but your antivirus software says otherwise?

Enter VirusTotal - "a free service for scanning suspicious files using several antivirus engines". Just send them a file, either through the web interface or e-mail, and they'll scan the file using antivirus engines from various companies, which includes:-

Here's a screenshot of a test I carried out:

Click to expand.

Because of the server load, I had to wait a few minutes before my request is processed. The results show that different antivirus engines give varying opinions about whether my file (IEHelp.dll) is infected or not - but when antivirus companies like McAfee and Symantec say it's safe, then it probably is. Therefore, this service is also useful to gauge the effectiveness of different antivirus solutions.