SAN FRANCISCO (AP) - It appears someone has a beef with Apple and Google - or at least the shuttle buses the high-tech companies use to ferry their workers to and from headquarters.

The shuttle buses transporting Apple and Google employees have been targeted by vandals.

Authorities in northern California say six buses have had windows broken with unknown objects while traveling on a highway south of San Francisco. On Tuesday, four Apple buses and one Google bus were attacked. Another Apple bus had a window smashed the week before.

The shuttles are unmarked, but the double-decker buses run by the high-tech firms are common in the San Francisco Bay area.

Some see the buses as a symbol of a system they believe has driven up rents - and increased the income divide.