How to fix “TCP/IP has reached the security limit…” event message

It could either be that you are actually wilfully establishing more than ten connections simultaneously (the actual establishing part that is, not total connections established) or you have some malware on the system.

As Izzy wrote this is supposedly a security feature to prevent malware from bogging down the system with incomplete connection attempts - so you may want to thouroughly check the health of your system first and try to find out what is causing this warning (try Malwarebyte's Antimalware if you want my personal favourite).

Some P2P applications might 'cause this, but most if you keep them updated should handle this by now. Here's the Microsoft article and here's some quotes from it, ending with an instruction in how you might find out the culprit:

The TCP/IP stack in Windows XP with Service Pack 2 (SP2) installed limits the number of concurrent, incomplete outbound TCP connection attempts. When the limit is reached, subsequent connection attempts are put in a queue and resolved at a fixed rate so that there are only a limited number of connections in the incomplete state. During normal operation, when programs are connecting to available hosts at valid IP addresses, no limit is imposed on the number of connections in the incomplete state. When the number of incomplete connections exceeds the limit, for example, as a result of programs connecting to IP addresses that are not valid, connection-rate limitations are invoked, and this event is logged.

At the command prompt, type Netstat –no Find the process with a large number of open connections that are not yet established. These connections are indicated by the TCP state SYN_SENT in the State column of the Active Connections information. Note the process identification number (PID) of the process in the PID column. Press CTRL+ALT+DELETE and then click Task Manager.