The numbers of PCs cleaned by Microsoft's anti-malware software worldwide during the second half of 2009 continued to trend upward, suggesting that more PCs are getting infected in total, according to the company's latest Security Intelligence Report (SIR).

The good news, though, is that Microsoft (NASDAQ: MSFT) also said that its launch of its new Security Essentials free anti-malware tools last September is helping it keep pace, helping it catch and clean infected PCs. .

Released this week, Microsoft's Security Intelligence Report Volume 8 (SIRv8) said that the company's software scanned some 500 million PCs worldwide in the second half of 2009. Of those, Microsoft caught and cleaned 1.7 million more infected PCs in the second half than it did in the first half of last year.

All told, the company cleaned a total of 41 million PCs between July and December. In contrast, between January and June 2009, Microsoft's software found and eradicated malware on 39.3 million PCs.

However, Microsoft's growing successes in removing malware from infected PCs comes against a larger trend of ballooning cyber threats and scams. Rival security vendor Symantec reported earlier this month in its own study that cybercrime continues growing at a blistering pace despite advances in PC and network security.

According to Microsoft's data, the largest increases of infected and cleaned PCs came in the U.S., which jumped 10.1 percent from the previous period, China, which rose by 19.1 percent, and Brazil, which gained 15.8 percent.

In the U.S., for instance, Microsoft caught 15.4 million infected PCs in the latest period as opposed to 14 million during the first half of 2009. By comparison, PCs in China accounted for 3.3 million cleaned infections in the most recent report, up from 2.8 million in the first half.

Meanwhile, Turkey, South Korea, and Italy showed the largest declines in infections, according to SIRv8. In absolute numbers, however, the declines don't seem so large. For example, infected PCs in Turkey fell by only 304,000, despite the fact that drop constituted a 26 percent decline.

Some categories of users are most at risk, Microsoft warned.

"Home users remain the most susceptible to infected malware and socially engineered threats, such as advertisements and personal assistance sites," Vinny Gullotto, general manager of the Microsoft Malware Protection Center, said in a blog post Monday.

So what can users do in order to help cut infections? A recently released third-party report by access lifecycle management BeyondTrust advocates tight control of administrators' privileges on corporate networks.

Upgrading operating systems can help as well, Microsoft said.

"The telemetry data in SIR has shown consistently that the lowest infection rates are seen on computers running Windows Vista SP2 [Service Pack 2] and Windows 7. Infection rates for both operating systems are less than half the infection rate for computers running Windows XP," Gullotto said in his post.

Additionally, he continued, users and administrators should keep up with antivirus definitions, as well as applying patches in a timely fashion.

"Analyzing the attacks in affected Office program installations, we found that most attacks affected Office 2003 users who had not applied a single Service Pack or other security update since the original release of Office 2003 in October 2003," Gullotto added.

Stuart J. Johnston is a contributing writer at InternetNews.com, the news service of Internet.com, the network for technology professionals.