Using URL Shortening Sites to Bypass Filters

Privacy Issues

Sites like Tinyurl.com and Bitly.com are the new go-to places for Tweeters who do not want long URLs to eat up their limited typing space. However, shortened URLs have another, more deceptive use. They allow spammers and hackers to bypass the old email filters and get into your inbox. Learn about URL shortening sites.

How can hackers use URL shortening sites

Most email anti-spam counter agents were created even before the use of embedded URLs in emails, not to mention shortened ones. Most current anti-spam programs trace back the URL to see if the site it originates from is dangerous. However, a shortened URL can be used by hackers in two distinct ways.

Hide a site under a trusted shortened URL

The first way is simple. They connect the site they want you to get directed to into one of the known and trusted URL shortening sites accessible for free to the public. Because the URL shortening site itself is trusted, the link is trusted. However, the link does not take you to the URL shortening site; it takes you where it was initially focused.

Fake URL shortening sites

Secondly, hackers can get even more creative. Once the email program’s anti-spam filters discover the misuse of the URL shortening sites, as some have already done, hackers generate their own URL shortening sites. Basically, they shorten a site that’s already shortened. So, when you click on the link, you get redirected not once, but twice. The first redirection is safe, the next is a hacker.

This was “yet another example of cyber-criminals adopting new technology to bypass traditional security measures,” said Bradley Anstis, vice-president of technical strategy at M86.

A lot of the traditional anti-spam engines were developed before Twitter, so they are not geared up to recognize embedded URLs as seen in blended email threats in spam, let alone shortened URLs that link to malicious or compromised Web pages,” Anstis said.

Some frightening statistics:

In May 2011, the global ratio of spam in email traffic from new and previously unknown bad sources increased by 2.9 percentage points since April 2011 to 75.8% (1 in 1.32 emails).

The global ratio of email-borne viruses in email traffic from new and previously unknown bad sources was one in 222.3 emails (0.450 percent) in May, a decrease of 0.143 percentage points since April. (From Net-security.org)

What can you do to defend yourself?

For one, never click on an email link if you do not trust the sender. Two, even if you do have confidence the sender, try to get to the link organically, meaning follow the standard method. If you are checking on a delivery, go to the main website instead of clicking on the link. These simple actions will help to keep your computer, and the information it holds, safe from hackers.

Author Bio:

This is a guest post from Laura Backes, she enjoys writing about all kinds of subjects and also topics related to internet providers in my area.  You can reach her at laurabackes8 [@] gmail.com.

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