Not sure if these will help, but here's some info on Welchia and general info on network traffic caused by worms:
http://securityresponse.symantec.com...chia.worm.html
http://securityresponse.symantec.com...rpc.worms.html
I guess if you keep your anti-virus definitions up to date and have your firewall setup right you'll be fine.
You may want to run an Internet-based virus scan like
http://housecall.trendmicro.com