Specific Media is actually #4 now. Based on May comScore, the rankings are:

1. Ad.com/Platform-A/AOL
2. Yahoo Ad Network
3. Google Ad Network
4. Specific Media

The company used “unique visitors” for the basis of its claim.

http://www.comscore.com/press/release.asp?press=1731

Here’s what they said:
Specific Media is the 5th ranked Ad Network (distinguished by the **) in the U.S. in September 2007 according to unique visitor count.

You mentioned that “The company, which claims to rank in the top 5 online ad networks”.

For the uninspired, what ARE the top 5 online ad networks? If Specific Media is to be in the top 5, what’s that based upon? Dollars? Impressions?

Interesting.