The site, inSpot.org, said more than 50,000 people have used the free service, which sends anonymous e-cards to notify past sexual partners that they should get tested for sexually transmitted diseases such as gonorrhea, syphilis and the human immunodeficiency virus, the disease that causes AIDS, CNN reported Tuesday.

The Web site is operated by a non-profit organization, Internet Sexuality Information Services.

Experts said that while the e-card notifications may seem insensitive, they are better than no notifications at all.

"When you weigh the importance of getting people notified, that's ultimately what needs to be done," said Jeffrey Klausner, director of STD Prevention and Control Services at the California Department of Public Health in San Francisco. "By notifying them -- even if it's done anonymously, even distantly, even with an e-card -- the benefits of getting someone diagnosed and treated outweigh the concerns of insensitivity."