NEW YORK (CNNMoney.com) - Stock options, a perennial thorn in the side of technology companies, have come back to haunt the sector in a big way.

Questions over stock option grants for executives have sparked federal investigations of more than a dozen companies, many of which are technology firms.

Shares of a number of tech firms including Brooks Automation and Vitesse Semiconductor have slumped in May compared to the Nasdaq average after getting caught up in a government probe into the backdating of stock options.

The list of companies under investigation for stock option grants is growing daily.

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A number of companies involved have fired top executives while others have resigned, and some firms said they may need to restate financial results going back several years. The list of companies getting swept up in the government probe grows daily.

Stock options give executives and employees the right to buy shares at a certain price, and if the stock rises after the options are granted, profits can be fat.

The SEC and prosecutors are investigating whether companies "back-dated" stock options for some employees, or retroactively changed the date an options grant was effective, to a date that led to a bigger windfall for those who held the options.

If that occurred, the companies could face accounting and tax problems - and charges that they violated securities laws.

The options being investigated were issued prior to passage of the Sarbanes-Oxley Act, which called for tighter disclosure requirements and reduced the potential for back-dating.

"It's unsettling to say the least," said Kevin Landis, portfolio manager of Firsthand Capital Management, a mutual fund firm specializing in tech stocks, of the scandal.

"It feels like there are a lot of companies out there that could get struck by lightning. Anyone who was really good at timing their options now has to explain how they weren't back-dating them."

Landis said the drama probably won't inflict broad damage to the tech sector as a whole, but for companies involved, the consequences could be devastating.

"You can have companies that could lose their management team just like that," he said.

One thing is certain: Any company that seems to have timed its options granting uncannily to coincide with a low point for its stock price is likely to find itself in regulators' cross-hairs.

Here's a look at who's been hit the hardest and who is under review.

UnitedHealth Group (down $0.73 to $42.09, Research), one of the nation's largest health insurance companies, said it may need to restate three years of results by as much as $286 million. The company has received a subpoena from the U.S. Attorney's office and a request for documents from the Internal Revenue Service, according to a brief statement on the company's Web site.

Brooks Automation (up $0.16 to $12.16, Research) The maker of products for semiconductor firms said Monday it received a subpoena from the U.S. Attorney's office regarding options. Last week, two board members resigned and renounced their stock options and restricted stock awards. Even before getting subpoenas, Brooks had said it would correct financial statements from fiscal 1999 to 2005.

Vitesse Semiconductor (up $0.07 to $1.87, Research) The maker of integrated circuits fired its CEO, CFO and another executive, all of whom had been put on administrative leave over "the integrity of documents" relating to the company's options grants.

The company revealed just days after that announcement that it received a subpoena from the U.S. attorney's office over option grants and was under investigation by the SEC. The company appointed a new slate of top executives and said it's conducting an internal investigation into the matter.

Comverse (Research) The CEO, CFO and senior general counsel of the communications software maker quit on May 1 and said they'll cooperate with a special committee of the board in its previously announced review of its option grants. The company said it will likely need to restate results, but it has not said to what extent.

Power Integrations (up $0.19 to $17.54, Research) The maker of high-voltage analog integrated circuits announced May 5 that its CFO and its board chairman both resigned; those resignations came about two months after Power Integrations announced it had created a special committee to review options grants. The company said it may need to restate financial results for 1999 through most of 2005.

Sycamore Networks (up $0.20 to $4.56, Research) The company, which makes optical networking products, said Tuesday that the SEC has launched a formal investigation related to options granted by the company from 1999 to 2001 that were erroneously accounted for.

American Tower (down $0.08 to $3.11, Research) The operator of broadcast and wireless communications sites said Tuesday it received a subpoena from the U.S. attorney's office requesting documents related to its option practices.

KLA-Tencor (up $0.25 to $39.32, Research) The maker of semiconductor manufacturing equipment was served by the U.S. Attorney's office regarding its options granting practices. Said the company's CFO, Jeffrey Hall, at J.P. Morgan Technology conference on Monday: "We take these (questions) very seriously. We're conducting an investigation led by an independent committee of our board of directors."

Juniper Networks (down $0.48 to $14.55, Research) The second-largest maker of Internet networking gear behind Cisco acknowledged Monday that it has received a request for information from the U.S. Attorney's office in New York relating to how it granted stock options. Juniper also said its board's audit committee is reviewing the company's option grants, with help from independent counsel and advisers.

Analog Devices (down $0.02 to $33.46, Research) The chipmaker said Wednesday it received a subpoena from the U.S. attorney's office over its options practices; the government requested records from 2000 to the present. Previously, the company announced that it reached a tentative settlement with the SEC regarding its option grants.

Other companies that have gotten requests for information from the government include RSA Security (up $0.37 to $15.44, Research), SafeNet (up $0.34 to $15.62, Research), and F5 Networks (down $2.34 to $45.94, Research).

Some firms, such as chip company Altera (up $0.85 to $18.99, Research) and software maker Quest Software (up $0.45 to $13.77, Research), have said they are conducting internal reviews.

Trident Microsystems (down $0.29 to $21.45, Research) also said it is conducting its own review following a story in Monday's Wall Street Journal noting that some options grants at the company preceded sharp run-ups in the company's stock price.

Analysts and investors are currently scouring the Street for companies that could be named next.

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