Popular Internet websites are a good place to advertise and therefore a target for spammers. Large throngs of visitors who view content on popular sites are the main draw. Spammers use vulnerabilities in message boards and forums to insert spam advertisements.

This “malvertising” is bad for the reputation of the website in question and because it opens up a Pandora’s box of security issues if a visitor decides to follow the link in the advertisement. In this short article we try to determine if certain subsets of the most popular 1 million Internet websites are more vulnerable to attack by spammers.

Experiment Goals

• Where are the spammers targeting their efforts?
• What kind of websites need to put more effort into stopping spammers?

Methodology

We obtained a list of the top 1 million websites from Alexa. We partitioned the list into 3 equal parts, designated as “top,” “middle” and “low” websites. From each subset, we randomly selected 1000 websites and determined if they were hosting spam advertisements.

To determine whether a site was hosting spam advertisements, we queried Google and other search engines with a list of keywords suggesting pharmacy spam (e.g. “buy Kamagra cheap” and “no prescription needed”). Once a website was found to include spam advertisements, the suspect pages from that website were downloaded to ensure that spam advertisements were indeed present.

Interesting Results

• The “top” tier was responsible for 9% of sites hosting spam ads.
• The “middle” tier was responsible for 4% of sites hosting spam ads.
• The “low” tier was responsible for 3% of sites hosting spam ads.

Conclusion

It is surprising to see that “top” ranking websites were more than twice as likely to have spam advertisements on their web pages than “middle” or “low” ranking websites.

It could be that spammers prefer to concentrate on the most popular sites versus the not-so-popular ones or that popular sites have more discussion/message boards that can be exploited. This question could be the basis of a more in-depth study of this phenomenon.

Examples of websites that host spam advertisements

Top sites:

www.pcd.go.th
www.blognone.com
www.howardforums.com
www.memeq.net
www.adrants.com

Middle sites:

www.rankarthai.com
www.pmg.org.za

Low sites:

www.nailshop.ro
www.simple-momreviews.com

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