To a great degree, Web browsers are the ultimate in computer convenience. The Internet started out as an academic information exchange enabler. Then Web browsers made the Internet easy to use and individuals to make use of the power of information exchange. In a few years, it has landed in nearly every corner and most homes throughout the World.
The convenience, productivity, and popularity of Web browsers make them a prime target for hackers and would be attackers. As the convenience of a product increases, so does the security risk, so Web browsers by their very nature should be expected to be risky. The productivity of the Web browser also makes it a prime target for attacks because the hacker can get the biggest strike for the effort put forth.
Finally, the popularity of a product plays important role by helping hackers increasing the scope of the attacks or vulnerabilities discovered. The hacker who develops an attack for a common Web browser is sure to find many vulnerable targets.