BBC News Online's Kevin Anderson in Washington

Every day brings more reports in the US of additional anthrax cases and newly discovered contaminated buildings in Washington, and demand for antibiotics to treat anthrax has skyrocketed.

Now, pharmacy trade associations and US Government agencies are investigating a myriad of websites that have sprung up to sell the antibiotic Cipro.

Officials say that some of the sites do not have a licence to dispense the medication in the US, and still other sites are under investigation for selling counterfeit versions of the drugs or alternative therapies that may not work.

Type Cipro into a search site, and a dizzying array of sites comes up. PillPrescribe.com, CiproPharmacy.com, 2-buy-cipro.com, and cipro-antibiotics-anthrax-vaccines.com are just a few.

Gas masks as well

Some sites urge caution. "Whatever you do, please do not attempt to self-diagnose or self-medicate with antibiotics as a precaution for anthrax," says a message on the homepage of CiproPharmacy.com.

US postal workers are given free antibiotics

At other sites, Cipro is just a click and credit card number away. One site says: "We carry many types of medicines in all categories normally obtained in many countries only with a prescription.

"It's simple, choose your product, go to the secure cart, make a credit card payment and that's it! We then ship immediately!"

Another site sells not only Cipro but also sends concerned shoppers an Israeli gas mask and a kit for safely opening suspect post.

Difficult enforcement

The Food and Drug Administration and the Federal Trade Commission (FTC) are now investigating many of these websites.

The FTC, an agency that monitors consumer fraud, was especially on the look out for sites selling counterfeit versions of the drug, or offering alternative therapies with questionable efficacy, a commission spokesman said.

The National Association of Boards of Pharmacy (NABP) has discovered some 50 sites that are selling Cipro.

But Carmen Catizone, executive director of the NABP, said the 50 or so sites it had found appeared to be backed by a core of a dozen companies.

Some sites used medical questionnaires or "cyberspace consultations" to determine whether a person should receive Cipro, said Mr Catizone, adding: "Some sites aren't even asking for that; you just pick the medication you want."

Foreign sites

The association is actively reporting these sites to state and local agencies. Cipro is supposed to be available by doctor's prescription only.

Masks and antibiotics are being handed out

The NABP is also seeing sites operated outside of the US, in Mexico, Canada and parts of Europe.

"None of those sites are approved or licensed to dispense medicine in the US. All of them are operating illegally," he said.

Mr Catizone admits that it will be a tough task to shut down these sites operating outside of the US.

"We have to ask for the co-operation of foreign governments, and it is not a major priority for these governments," he said.

Lifestyle drugs

When these sites started, they were primarily selling lifestyle drugs such as the anti-impotence drug Viagra.

"It is hard to get people to see there is a crisis happening when middle-aged men are ordering Viagra," he said, but added that this time the threat was greater.

For those who do have a doctor's prescription and want to buy online, the NABP has a list of online pharmacies that have passed its certification programme.

However, health officials fear that many consumers who turn to the sites that put profit over public health concerns will find themselves a pound poorer and not at all healthier.