Updated from 11 a.m.

OKLAHOMA CITY -- WellCare ( WCG) shares lost as much as two-thirds of their value on Thursday following a government raid of its offices

The government has launched a massive investigation of the company, which supplies health insurance coverage exclusively to Medicare and Medicaid recipients. Among others, the Federal Bureau of Investigation and the Medicaid fraud unit for the state of Florida - the company's largest market - participated in the sweep.

So far, few details have emerged. However, because the probe involves both federal and state authorities, it could threaten WellCare's Medicare and Medicaid businesses alike. Experts feel especially concerned about WellCare's Medicaid business in Florida , since it generates up to one-fourth of the company's earnings.

"In the worst-case scenario, if WellCare were convicted of a criminal offense, it would be technically unable to contract with state or federal governments - effectively putting all of its existing contracts and its entire revenue and earnings stream into jeopardy," CIBC World Markets analyst Carl McDonald wrote on Wednesday. However, "it is extremely rare that this worst-case scenario comes to pass.

"More likely," McDonald added, "we think the market will focus on what WellCare's earnings stream would look like if it were to exit the Florida Medicaid business (and estimate) a total negative stock price impact of $35" a share.

When it reopened after being halted on Wednesday, however, WellCare's stock actually fell by twice that much. At a recent $44 and change, the shares are now trading at lows unseen in more than a year.

Some WellCare insiders managed to escape that crash. Director Neal Moszkowski executed the most recent transaction, selling more than $1 million worth of stock four days before the raid. Meanwhile, WellCare CEO Todd Farha has been unloading company stock for months. He executed his last big transaction, which generated more than $1 million as well, just two weeks ago.

For its part, WellCare likes to stress that Farha and other insiders have adopted prearranged selling plans meant to prevent improper trading. Moreover, both men continue to control large amounts of stock.

But Taxpayers Against Fraud, an organization that promotes whistleblower lawsuits against government offenders, still questions the timing of those sales.

"Maybe these were legitimate transactions," admits Patrick Burns, a spokesman for the organization. "But my thoughts on this are sort of simple: If people are selling $1 million worth of stock right before a government raid, then they are going to have some explaining to do."

Shares fell $72.53 to $44.64.