Google, on the other hand, leads in search ads, which are usually cheaper, plain text ads linked to a destination website and whose display is triggered by the topic of search queries or of Web pages in participating publisher sites.

However, Google has been trying for years to make a strong push into premium display advertising and has invested billions in this effort, including its acquisitions of DoubleClick and YouTube, and has started to see progress in the past year.

Thus, it's not surprising to see Yahoo pursuing acquisitions to help it protect and boost its presence in this space, which is key to its financial stability and potential future growth.

5to1 founders include former Fox Interactive executives James Heckman, who is 5to1's CEO, and Ross Levinsohn, who left 5to1 to join Yahoo as executive vice president for the Americas region in October of last year.