On a single day last week, Lee Enterprises, the company that owns the St. Louis Post-Dispatch and dozens of other newspapers, received 2.86 million e-mails. At least 96 percent of them were spam. The deluge of spam is an aggravating — and expensive — fact of life at corporations across America.

Lee spends about $100,000 a year trying to filter the junk mail from its employees' electronic mailboxes, where it sucks up time, diminishes productivity and drives people nuts. Even with filters, "I have people complain that they get too much spam," says Tom Jackson, Lee's network administrator.

Spammers and corporate tekkies have spent years playing a virtual game of cat and mouse. Every year the cats try to build better mousetraps, but the mice still are winning.

Spam volume has nearly doubled in the past year, according to people who run anti-spam programs. The scams have moved beyond phony pitches for Viagra and letters from Nigerian generals offering to move millions into your bank account. Lately, cyberspace has been deluged with old-fashioned "pump and dump" stock schemes: Spammers buy stock in obscure companies, then fill mailboxes with pitches touting the stock as a sure winner. When suckers buy shares, they drive up the price. Then the spammers cash out, the stock price plunges and the suckers lose.

In 2003, Congress passed the Can-Spam Act, threatening spammers with jail. Spam declined for a while, but only while the spammers moved abroad. Pitches today often originate in Europe, South America and Asia. China is now a major spam exporter. If all those countries passed their own Can-Spam laws, the spammers would set up in Tonga or Vanuatu. Any outpost with a high-speed Internet connection can generate spam.

Companies use two main methods for filtering out spam. First, they block all mail from known spammers and Internet service providers who help them. Then they electronically scan the mail for patterns indicating spam or many identical messages.

Spammers are getting around the pattern-scanners by embedding their written pitches inside pictures, which are difficult to scan. They also take up much more room on the victims' systems.

Spammers also trick unsuspecting people into installing "malware" on their personal computers. The programs turn computers into "zombies" sending out mail at the spam-master's command, without the computer owners' knowledge. Armies of such zombies fire off spam from addresses not suspected of spamming, and they sail right through the filters.

The cats haven't given up on their mousetraps. One suggestion, called "hashcash," would provide an electronic "postage stamp" vouching for the mail's legitimacy. To get the stamp, a sender's computer would have to perform a mathematical calculation taking a fraction of a second. That's no problem for an innocent e-mailer, but it would seriously stall spammers sending out e-mail by the millions.

Given time, spammers will foil that trap as well. Perhaps the best way to stop spam is to educate consumers. Spammers will stop spamming when nobody can be fooled anymore.