After tricking several thousand executives into downloading malicious software earlier this week, online scammers started up their subpoena phishing scam again on Wednesday, but on a much smaller scale.

First reported on Monday, the phishers send a small number of emails to senior executives within companies, often CEOs, telling them that they've been subpoenaed for a federal court case. The emails direct the victim to a website that is very similar to a legitimate California federal court page, but ending in '', rather than the '' web domain actually used by federal courts.

Although they end with the same letters, the domains used in this scam are actually different from and not connected with the website, which offers access to court records in some jurisdictions.

The email sent to executives is specially crafted to appear legitimate, a tactic called 'spear-phishing'. The emails include the executive's name, company's name and even the correct phone number.

Executives who click on the link in the email are then told that they need to download a plug-in in order to read the subpoena. That plug-in is actually malicious software.

Although the US federal court system uses email to communicate information about cases, subpoenas for new cases are not served via email.

Verisign, which estimates that about 2,000 people were tricked by the scam on Monday, believes that Wednesday's attack was on a much smaller scale. Late Wednesday the company's iDefense group had tracked only about 100 infections, said Matt Richard, director of iDefense's Rapid Response Team.

Security experts have been fighting the phishers. By Tuesday they'd managed to get the first phishing website taken down, only to have the second one pop up on Wednesday.

Because the attack targets such a small number of victims, antispam companies have had a hard time filtering the emails; antivirus companies have been similarly pressed to block the malicious software that the attackers are using.

Yesterday, antivirus companies weren't blocking this latest version of the malware, said John Bambenek, a security researcher at the University of Illinois at Urbana-Champaign and volunteer at the SANS Internet Storm Center.