Browsing Problems

Hi All

A friend is experiencing a weird problem on his MacBook - here's an extract from the email he sent me. Anyone have any ideas what i might be?

"With the Mac I checked for OSX updates and let them install, and then checked for Parallels updates and let them install. Now after going between three or four web pages the browser just stops. The pinwheel is going but nothing else happens, then the computer says it needs to restart. The odd thing is this happens with either firefox or safari. I restart, after three or four pages, the same thing happens. At least the problem is reliable!"