Opera uses network bandwidth with no windows open

[flyingrhino]

I've noticed that Opera for windows v7.52 uses 25-30% of my dialup bandwidth and there are no windows open. I checked this using the task manager networking tab on windows xp.

I close opera and the network usage goes back to zero.

Any ideas ?

I test for spyware and viruses regularly and have none.

[serrebi101]

Doesn't the free version of opra display adds?