Software Giant, Microsoft and drug company Pfizer are taking aim at those advertisements for fake Viagra that constantly flood in-boxes. The two companies yesterday announced they had filed 17 lawsuits against online pharmacies they say sent hundreds of millions of unwanted e-mail ads, or Spam, to users of Microsoft's Hotmail e-mail program last year alone. Pfizer and Microsoft filed parallel lawsuits against two international Web sites -- CanadianPharmacy and E-Pharmacy Direct -- that sell illegal versions of Pfizer's Viagra. The companies claim they hope to lower the number of junk mails people receive in their inboxes. With health, sexual aid drugs and pornography being the most popular subjects for spam messages. "If you've ever received unwanted spam, you've probably received spam about Viagra," said Microsoft attorney Aaron Kornblum.