Those unsolicited e-mails promising low-cost Viagra, cheap herbal alternatives for sexual health or “male enhancement” pills are losing their luster among spammers, according to a new security study by Microsoft.

In the second half of 2008, the volume of spam for sexual medications fell a dramatic two-thirds from the first half of the year. Spam for Viagra, Cialis, Levitra and other erectile dysfunction medications had topped the list of spam messages from January to June 2008, making up more than 30 percent of the total volume. In the second half, the volume dropped below 10 percent.

Mirroring the drop in sexual medication spam is a drop in the volume of sexually explicit and dating solicitations via spam, according to Microsoft.

People still have sex and prurient interests, but the sudden and dramatic shift in sexual spam volume may be a reflection of deteriorating economic conditions and shifting economic priorities.

Replacing sexual medication spam at the top of the list is non-sexual medication messages, which nearly doubled in the second half of 2008. Spam for blood pressure, hair loss, antihistamines, vitamins and alternatives to expensive branded drugs shot up from 20 percent in the first half of 2008 to more than 40 percent in the second half of the year.

A reflection of changing priorities as a result of the recession is seen in the volume of stock and financial services spams, which went from slightly more than 5 percent of the total spam volume in the first half of the year to being practically nonexistent following the fall market crash. Nevertheless, the recession had no impact on “get rich quick” scams, which saw a slight uptick.

According to the Microsoft report, spam and unsolicited messages continue to make up all but 3 percent of the total e-mail traffic volume worldwide.

In a separate report issued this week by Symantec, spam is the second—computer and Internet-borne viruses top the list—security concern among small and midsize businesses. Of businesses with 10 to 500 employees surveyed by the security vendor, 71 percent are somewhat or extremely concerned about unsolicited e-mails.

Conversely, Symantec’s survey found that 42 percent of small and midsize businesses have no anti-spam protection for their endpoints or e-mail servers.