In its quarterly analysis of the security software running on 43,000 computers around the world between March and May 2011, OPSWAT found that well-known brands such as McAfee, Symantec and Trend Micro are continuing to be pushed down the popularity tables by mostly European rivals marketing on the basis of either a free-to-use or "freemium" (free with paid upgrades available) model.

Globally, the two most commonly encountered brands were Czech companies Avast Software and AVG, tied with being detected on 12.3 percent of systems each, ahead of Avira of Germany on 12.2 percent, Microsoft on 11.2 percent, and ESET Software, also of Germany, on just under 10 percent. Traditional security brand leaders, Symantec, McAfee and Trend Micro were found on only 8.77 percent, 4.5 percent and 2.15 percent of systems respectively.

In terms of individual products, the most popular program was Microsoft's Security Essentials with 10. 6 percent market share, ahead of Avira's Antivir Personal Free with 10.2 percent, Avast Free Antivirus with 8.66 percent, and AVG Antivirus Free with 7.92 percent.

The most common subscription antivirus programs were Eset Software's Nod32 Antivirus with 7.25 percent, Kaspersky Lab's Internet security with 4.31 percent and Norton Antivirus with 4.3 percent.

The rise of Microsoft Security Essentials has been particularly striking in North America, where according to OPSWAT it is now found on just over 15.7 percent of PCs, ahead of AVG on 10.4 percent and Avast on 7 percent. Even here, however, the European upstarts have gained traction, with ESET Software, Avira, and AVG easily making into the top 10 of most common antivirus applications.