Symantec Thursday said that "suspicious behavior" by a captured exploit had led it to mistakenly conclude that the most up-to-date standalone versions of Adobe System's Flash Player are vulnerable to ongoing attacks from Chinese servers.

But a Symantec researcher said earlier Thursday that Flash Player 9.0.124.0, the currently-available version of the popular multimedia player, is not vulnerable to the ongoing attacks. Just yesterday, Ben Greenbaum, a senior research manager in Symantec's security response group, had claimed that while Flash Player 9.0.124.0 plug-ins were safe, standalone editions of the program were not.

"All versions Version 9.0.124.0 on all platforms, plug-ins and standalone, are not vulnerable," Greenbaum said Thursday.

The switch was the third change in Symantec's analysis in the last two days.

On Tuesday, Symantec first warned that legitimate Web sites were redirecting unwitting users to one of several Chinese servers, which in turn were trying multiple exploits, including some aimed at Flash Player. Then, Symantec said that older versions of the Adobe software -- version 9.0.115.0, which was replaced in early April -- and the current 9.0.124.0 could be successfully exploited.

Based on that analysis, Symantec dubbed the vulnerability a "zero-day" bug, meaning it was unpatched, and dangerous to anyone with Flash installed.

Later on Tuesday, however, Symantec backtracked from the zero-day label. "Originally, it was believed that this issue was unpatched and unknown, but further technical analysis has revealed that it is very similar to the previously reported Adobe Flash Player Multimedia File Remote Buffer Overflow Vulnerability (BID 28695), discovered by Mark Dowd of IBM," Symantec said.

Even so, Greenbaum maintained yesterday that while the vulnerability wasn't new, the in-the-wild exploit was effective against standalone versions of Flash Player 9.0.124.0. "Not all the versions are patched correctly," he said Wednesday.

Thursday, however, Greenbaum said that Symantec had come to the erroneous conclusion based on tests of the standalone Linux version of Flash Player 9.0.124.0. "While testing against the latest [Linux] version, we saw behaviors consistent with a successful exploit that failed to deliver the payload," he explained Thursday. "[But] the exploit was not, in fact, successful against the latest version."

In a follow-up e-mail, a Symantec spokesman spelled it out in more technical detail. "The latest Linux player, when used to open the exploit file, would abruptly exit silently," said the spokesman. "Stack analysis revealed several internally-handled segmentation faults, which is not normally desired behavior for a program." That behavior, in fact, is often a sign of a successful exploit that then uses incorrect offsets or payload code, he added.

"Further research was unable to produce a successful full exploitation and Adobe confirmed that what we had observed was in fact expected and by design," the spokesman said.

For its part, Adobe stuck to its Wednesday claim that the current Flash Player 9.0.124.0 is not vulnerable. "This exploit does not appear to include a new, unpatched vulnerability as has been reported elsewhere," said Adobe spokesman Mark Rozen. "Customers with Flash Player 9.0.124.0 should not be vulnerable to this exploit."

Greenbaum said that spurious results on Windows test systems had also contributed to Symantec's claims that some versions of 9.0.124.0 were at risk. "We were also seeing compromises on the Windows side," he admitted, "on the latest version of Flash that we downloaded from Adobe's site." Later, Symantec's researchers realized that they had not downloaded an additional patch; when they did and retested, they found the Windows edition to be safe.

"We apologize for the confusion," said Greenbaum. But he defended the analysis, noting that changing updates are common in the security trade as researchers spend more time investigating a problem.

Adobe has recommended that Flash users double-check the version they're running and update to 9.0.124.0 if necessary. Adobe maintains an About Flash Player page that displays the current plug-in version from any browser. Users, however, must run the check for each installed browser.