Boston based private equity and venture capital investment firm, Summit Partners today announced that it has invested $100 million for a minority stake in AVAST Software, makers of the world’s most popular antivirus software.

AVAST, with over 100 million users worldwide, utilizes a ‘freemium’ business model, which offers a full-fledged free product with a premium option.

“After writing a program to remove the Vienna virus back in 1988, it was about six months before I saw another virus. Now our Virus Lab adds 3,000 new virus samples a day to its database,” said Mr. Baudis, AVAST Software virus guru. Security and data protection services firm Sophos, In the first half of 2010, claims to receive an average of 60,000 new malware samples every day, about 1 every 1.4 seconds.

Scott Collins, a Managing Director of Summit Partners who will join the AVAST Software Board of Directors.

Summit Partners has made other notable investments in the security market including McAfee (to be acquired by Intel for $6.6b, Postini (acquired by Google), SafeBoot Holdings BV (acquired by McAfee), and Sybari Software (acquired by Microsoft).