Kaspersky is dealing with a fairly large "oops", after a botched update led to some Windows machines having Explorer.exe quarantined. Every once in a while, a false positive will pop up in anti-spyware or anti-virus suites. Sometimes they end up crippling other software, but in this case it ended up crippling the operating system itself.
The glitch was not widespread, but might lead to concerns over the reliability of the suite. It is the second flaw in a week that led to trouble after an update. Kaspersky is of course saying they will review their testing procedures to find out why the slip-ups have been occurring. That said, if you happen to use the suite and now have a dead system you probably know why.