It has been reported by one of our customers that they have developed an SSIS package which needs to connect to an FTP Server on their internal network to download some files and take some data from the files to put it into some destination like a SQL Server table after doing some conversions/calculations etc.
But the FTP Server connection was failing when they tried connecting to FTP Server within SQL Server Business Intelligence Studio (BIDS). On the other hand, when they tried connecting to the very same FTP Server using "ftp" command from a command line it was working without issues. They also can connect to the FTP Server from Internet Explorer. It was looking quite strange to me ...
After doing lots of tests, we've found out that the antivirus software installed on the machine was blocking the FTP traffic! We removed this FTP traffic blockage within the antivirus software and package started to work without issues.
Don't you also think like me that the antivirus softwares are trying do a lot more than we expect them to do ? I can hear your voice saying "But the virus writers are adding new techniques to the viruses day by day and some of them can try to reach an FTP servers on the net ? ". Ok that's true. But the viruses also can do the lots of similar things over HTTP. Ain't it ? They are already doing such things a lot. Will we block HTTP traffic too ? ;)