A new round of greeting card spam that draws users to attack sites relies on a sophisticated multi-pronged, multi-exploit strike force to infect machines, security professionals said late Thursday.

Captured samples of the spam have all borne the same subject line -- "You've received a postcard from a family member!" -- and contain links to a malicious Web site, where JavaScript determines whether the victim's browser has scripting enabled or turned off.

"If JavaScript is disabled, then they provide you a handy link to click on to exploit yourself," said an alert posted Thursday afternoon by SANS Institute's Internet Storm Center (ISC). Some users turn off scripting because it is a frequent attack vector; browsers with JavaScript enabled are simply fed a two-part package of downloader and malware.

The quick browser status exam in this attack is somewhat similar to one used in a different exploit tracked by Symantec since Tuesday, but the two are not connected, said Oliver Friedrichs, director of Symantec's security response group. "They're using two different toolkits," said Friedrichs, "but they're both prime examples that exploits against browsers are more and more prevalent."

Thursday's greeting card gambit tries a trio of exploits, moving on to the second if the machine is not vulnerable to the first, then on to the third if necessary. The first is an exploit against a QuickTime vulnerability, the second an attack on the popular WinZip compression utility and the third, dubbed "the Hail Mary" by ISC, is an exploit for the WebViewFolderIcon vulnerability in Windows that Microsoft Corp. patched last October.

ISC said several antivirus vendors had tentatively pegged the executable malware -- the file offered to users whose browsers have JavaScript disabled -- as a variation of the Storm Trojan, an aggressive piece of malware that has been hijacking computers to serve as attacker bots since early this year. According to ISC's warning, computers already compromised by Storm -- a.k.a. Peacom -- are hosting the malware, and the attackers are rotating those machines' IP addresses in the spam they're sending.

"Every Storm-infected system is potentially capable of hosting the malware and sending the spam, but only a few will be used in any given run," said the alert, "depending on how many e-mails they want sent and how many Web hits they're expecting."

Hackers haven't abandoned the practice of attaching malware to e-mail, then counting on naive users to open the file, said Friedrichs. But malware hosting sites are the trend. "It's much more difficult to send a full malicious file," he said, because of users' learned reluctance to open suspicious files and filtering and blocking tactics by security software.

"This is widespread, and leads the user to multiple IP addresses," said Shimon Gruper, vice president with Aladdin Knowledge Systems, a security company known for its eSafe antivirus software. "There's not a single server, there are multiple exploits [and the e-mail] has no attachments. This will be very difficult to detect."

Two days ago, a Symantec honeypot captured a similar Web site-hosted attack that had an arsenal of multiple exploits at its disposal. That attack, however, featured an unusual, if rudimentary, browser detector that sniffed out whether the target computer is running Microsoft's Internet Explorer (IE) or Mozilla's Firefox. If the attack detects IE, it feeds the machine a Windows animated cursor exploit. If it finds Firefox, however, the sites spits out a QuickTime exploit.