Microsoft's latest security report shows that the number of new vulnerabilities found in its software was lower in first half of the year than the last half of 2007, with the Windows Vista OS proving more resistant to exploits than XP.

Microsoft reported 77 vulnerabilities from January to June compared to 116 for the last six months of 2007, according to the company's fifth Security Intelligence Report.

The decline is in line with the software industry as a whole, which saw a 19 percent decrease in vulnerability disclosures compared to the first half of 2007, Microsoft said. However, those vulnerabilities considered highly severe rose 13 percent.

Exploit code was available for about a third of the 77 vulnerabilities; however, reliable exploit code is available for only eight of those 77.

Other data shows that XP is attacked more frequently than Vista. In XP machines, Microsoft's own software contained 42 percent of the vulnerabilities attacked, while 58 percent were in third party software. For Vista machines, Microsoft's software had 6 percent of the vulnerabilities attacked, with third-party software containing 94 percent of the flaws.

New security technologies such as address space randomization have led to fewer successful attacks against Vista, said Vinny Gullotto, general manager of Microsoft's malware protection center.

"Moving onto Vista is clearly a safe bet," Gullotto said. "For us, it's a clear indicator that attacking Vista or trying to exploit Vista specifically is becoming much more difficult."

The highest number of exploits were released for Windows 2000 and Windows Server 2003 operating systems, Microsoft said.

Hackers appear to be increasingly targeting Internet surfers who speak Chinese. Microsoft found that 47 percent of browser-based exploits were executed against systems with Chinese set as the system language.

The most popular browser-based exploit is for the MDAC (Microsoft Data Access Components) bug that was patched (MS06-014) by Microsoft in April 2006.Some 12.1 percent of all exploits encountered on the Internet targeted that flaw. The second most encountered exploit is one aimed at a vulnerability in the RealPlayer multimedia software, CVE-2007-5601.

The two most commonly exploited vulnerabilities in Windows Vista concerned ActiveX controls that are commonly installed in China, Microsoft said.

Gullotto said Microsoft is continuing to improve the Malicious Software Removal Tool (MSRT), a free but very basic security application that can remove some of the most common malware families.

Last month, Microsoft added detection for "Antivirus XP," one of several questionable programs that warn users their PC is infected with malware, Gullotto said. The program badgers users to buy the software, which is of questionable utility. "Antivirus XP" is also very difficult to remove.