MSN last week quietly asked U.S. testers of adCenter, its new pay-per-click advertising platform, to spread the word about testing the service on their sites; when of them posted the email invitation from MSN on his blog, SVP of MSN Information Services Yusuf Mehdi himself made the announcement on the MSN Search blog, writes InternetNews. MSN is looking for small-to-medium-sized businesses to take part in the self-service offering, but the pilot remains by invitation only, with Microsoft selecting participants from among applicants.

During the U.S. pilot, MSN adCenter will deliver text-based advertisements on up to 25 percent of MSN Search traffic, Mehdi said. The rest will will be served through MSN's partnership with Yahoo.

Advertisers using adCenter will be able to make their keyword buys by geographic location, gender, age group, lifestyle segment and time of day. MSN adCenter, expected to officially launch later this month in the U.S., uses data from Microsoft's Passport registration and purchased demographic information.

Previous stories:

- MSN's AdCenter to Be Total Ad Management Platform

- Microsoft to Sell its Own Search Ads, Challenge Google

- MSN Buys Net-Phone Startup; Pay-per-Call Possible for adCenter

- Gunning for Google: MSN Reveals Paid Search Plans