NEW YORK (CNN/Money) - Tired of weeding through scores of e-mail offers for herbal alternatives to Viagra and URGENT REQUESTS FOR ASSISTANCE from newly solvent relatives of recently deceased African politicians?

Spam sucks. And according to a recent report by tech research firm Gartner, about half of the average business e-mail box contains spam, and less than 10 percent of companies have effective spam-filtering technologies.

So it's no wonder then that some small tech firms that offer anti-spam solutions are up big this year. Shares of Tumbleweed Communications (TMWD: Research, Estimates), which makes the E-mail Firewall anti-spam software, have surged 290 percent year-to-date. And shares of a company called Zix (ZIXI: Research, Estimates), which makes ZixMail, are up nearly 70 percent.

Tumbleweed has a big presence in the financial services area, with customers such as J.P. Morgan Chase and mutual fund firm American Century, while Zix caters mainly to the healthcare market, with customers such as Humana and Pacificare Health Systems.

"The corporate market is where the big demand for anti-spam is," said Gary Craft, an analyst with Financial DNA, an independent research firm specializing in financial technology companies. "Companies want to protect their employees from being bombarded with this malarkey." Craft owns shares of Zix.

Craft estimates that the total market for anti-spam and content filtering, as well as related areas such as secure delivery of e-mail and file attachments, is about $1 billion this year and that it's expected to grow at about a 25 percent clip annually for the next few years.

Sure, the market is incredibly crowded. There is loads of competition from private companies such as Brightmail, Firetrust (which makes Mailwasher) and the marvelously named iHateSpam from Sunbelt Software.

In addition, the big three publicly traded antivirus software firms, Symantec, Network Associates and Trend Micro, have anti-spam products as part of their broader suites as well.

Still, it appears that there is plenty of opportunity for both Tumbleweed and Zix, which have trailing 12-month sales of just $25 million and $1.7 million respectively.

"This is likely to remain a fragmented market," said Paul Ritter, an analyst with Yankee Group, a tech research firm. "There will be some acquisitions but I don't see this as a massive rollup opportunity for larger software players."

So are either Tumbleweed or Zix worth investing in now, given their big runups? Investors should proceed with caution.

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Tumbleweed (market cap: $229 million) is not expected to post a profit in 2003 and is trading at 41 times 2004 earnings estimates, which seems a bit pricey. However, analysts are expecting earnings to grow at about a 25 percent clip for the next three to five years. Analysts are predicting a 57 percent increase in sales in 2004 as well.

Zix (market cap: $180 million) has no Wall Street analyst coverage, which makes it tougher to value. Sales nearly tripled in the second quarter from a year ago but the company is still losing money.

So Tumbleweed and Zix might be due for a bit of a pullback, considering the strong runs their stocks have already enjoyed this year. But both companies are worth keeping an eye on. As long as spam remains a big problem for corporate e-mail users, that should translate to more business for both companies.

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And despite more anti-spam legislation, such as the bill that California Governor Gray Davis signed last week that calls for fines of up to $1 million against businesses sending spam to California residents, it's doubtful that spam will grind to a halt.

For one, anti-spam laws such as California's are likely to be challenged on freedom of speech grounds. Also, the fact that a fair amount of spam is generated outside of the U.S., will make it tough for states to enforce the laws.

"Legislation will not displace the need for anti-spam software," said Ritter. "There is a strong need for it and that need will be around for several years."

If you don't believe that, then can I interest you in some great savings on human growth hormone? I'm sure I have an e-mail or twenty that I can forward.

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